Im want to replace my good, old TP-Link TL-WR841N/ND v9 with either Netgear R6220 or GL-AR750S.
Both are 128 flash, so it should be OK for future OpwnWRT releases.
Different SoC though: MT7621ST vs Qualcomm Atheros QCA9563?
What would be a better choice nowadays?
https://openwrt.org/toh/netgear/netgear_r6220
https://openwrt.org/toh/gl.inet/gl-ar750s
I am using a Netgear r6220 and archer c7 v5, very similar to the ar750s. Both are fantastic. You can't go wrong with either.
OpenWrt 19 only will support 32 devices on the ath10k device though, unless you edit a text file on the router. There are instructions on the forum somewhere, but you may consider that a downside.
The mt76 target apparently has less of a firmware blob, which may be considered an advantage in terms of future support.
I'd go with the r6220 myself for that.
The MT7621 is arguably the more powerful SoC of both. Newer MIPS, higher clock, and dual instead of single core.
Thank you very much for all advises. Appreciate.
In the mean time I have found also at: Linksys WRT1900ACS
https://openwrt.org/toh/linksys/linksys_wrt1900acs
Much more expensive but offers: 128/512 MB, SoC: Marvell Armada 385 88F6820
Im wondering about this one as I want to choose device for years (next 5 at least) and keep it with the most recent OpenWRT.
Any hints/advises/recommendations very welcome, thanks 
You don't. The SoC is fine but nobody knows how the wireless will be (the mwlwifi driver has not seen any updates for over a year).
You want enough flash and RAM, sure, but you should look at the WAN speeds you expect to have. To go from a cheap TP-Link MIPS device to a top shelf ARM one is quite the jump. If you made do with that TP-Link, you should be asking yourself: what do I need? Not what makes your eyes blink.
If you need higher throughput you can look at ipq40xx or ipq806x devices. Or even x86.
There are a few threads around already that should offer you some insight, but you should formulate a clear list of your requirements, see the wiki page for tips on that.
It has closed source firmware with bugs. The company that made the soc was bought a while back and no new fixes have come forward. There are known issues with some IoT devices and wpa3 cannot happen. It's decent hardware, but locked behind abandoned closed firmware.
Besides, in a few years you'll probably want a wifi 6e device anyway. Get one of these more open devices that can support wpa3 and enjoy good WiFi for the next few years.
Thanks guys for your replies.
Here is my check list:
It feels like r6220 would do the work.
Though I just read somewhere on the forum that MT7621 is about to be deprecated soon...
Can you recommend anything reliable based on my check list?
By deprecated,do you mean no longer manufactured or no longer supported.
If you mean no longer manufactured, that doesn't matter as long as openwrt keeps supporting your device.
I think he/Diizzy meant longer manufactured.
Don't bother with MT7621 devices, they're slow and more or less deprecated by now as the majority of vendors are moving to ARM instead of MIPS.
mt7621 is still in production, but it's one of the last remaining (new'ish) mips SOCs, although it also already has a successor with the ARMv8 based mt7622 (the ARMv7 based mt7623 seems to be abandoned). For 802.11ac based devices, vendors appear to have skipped mt7622 so far (probably because of "never change a running system" and likely to save costs for re-designing the devices). For 802.11ax, I expect mt7622 to become more prevalent - all other major SOC vendors (aside from Realtek) however have made the switch from mips to ARM already.
What diizzy is (likely) referring to, is mips as a whole. For almost two decades mips was the SOC used in (almost) all routers (cheap, no longer useful for workstation performance, but it did inherit very good I/O abilities and performance from that legacy (SGI et al)), however very little development has happened since then (actually, mips based SGI workstations were already 64 bit based in the early 90s, mips based router SOCs are still 32 bit based), the clock frequency has barely doubled to tripled in 15 years, ISA and CPU performance per cycle are largely identical. It is safe to say that mips as a platform has stagnated (for a long time it was still good enough, but now with increasing WAN speeds the world is changing, while mips had been in hibernation) and is in the process of being replaced by ARM.
On the CPU side and its processing performance, ARM has gotten a lot faster than mips - and vendors like to standardize on one CPU platform (where they can re-use their mobile/ smartphone SOCs, little-endian, same drivers, etc.). For a long time the I/O side of it, especially for the smartphone derived SOCs, had been neglected to some extent, but this situation is changing (especially for ARMv8).
At this point it's therefore difficult to recommend mips for new devices, as modern ARM devices bring more to the table for similar prices - mips is basically dead (only kept on life support for cheap entry level devices).
Edit: just to clarify, both if your examples (ath79 and mt7621) are mips based.
Alright, so if I understand correctly I should rather look for devices based on ARMv8.
I guess there is no way to filtered out ToH for ARMv8.
However it should be possible by CPU and/or Target.
mt7622 - is one example then.
Any other ARMv8 SoCs that u would recommend or maybe device to recommend?
Thanks Tmomas, followed your link i generated this one showing also memory (that's important).
Any recommendations?
To me Linksys WRT1900ACS still looks attractive but is was already said by Dana44 it is closed source firmware with bugs 
I recommend using SQM. It will reduce latency, however neither router has a cpu that can do SQM at the speed you'll go to down the road. They're good for where you today. You'll probably want to get a new wifi6e router then anyway. 
Re: MIPS vs arm vs x86 vs PowrPC. It doesn't matter. The code is written in C and compiled into whatever flavour ISA you like. There are fast and slow versions of all hardware. Looking at the two routers they have roughly equivalent performance and MIPS vs ARM doesn't come into play.
If you're looking for long term support look for what is open. Ath9k was the last open system and is still supported and has features that haven't made it into anything else yet!
It still has fixes going in when problems are found even though people have moved on to ath11k development!: https://marc.info/?l=linux-wireless&m=158597395223128&w=2
This can't happen on closed source stuff like the NXP/Marvell/Linksys. And partially is the case with ath10k. There was a recent switch to ath10k-ct firmware (firmware from candelatech instead of direct from vendor) because ath10k-ct has development and there isn't much with regular ath10k firmware. However ath10k-ct has enough bugs in the current release some people started switching back to the old ath10k! If it was open like the ath9k somebody would've addressed them already.
The ath10k bugs are in unusual situations - I just use it as an illustration of why open is best and I recommend the mt76 routers in 2020. IMO mt76 simply is more likely to have continued support.
Both are solid choices. Flip a coin! You'll be happy with either.
You need to take a step back (again) and find out your actual needs, now and what you expect to happen in terms of potential WAN speed upgrades in the immediate future (not more than ~3 years). Then find an affordable option matching those requirement Overspec'ing beyond that is just too expensive and rather unreasonable at this point (the is a lot of upcoming development in the router market). Economically you'll get better results by buying an 80-160 EUR/ USD (or less, if your connection allows it) device matching your requirements now - and to defer upgrading the device to when you need it, in 4, 5 or more years (now you'd just be severely limited in your available option and also pay a premium for features you won't need for that very same time span).
As mentioned before, mt7622 isn't really available yet (it will, probably with the introduction of Mediatek's 802.11ax lineup (mt7915)).
The only ARMv8 devices on the market right now, would be the mvebu 3700/ 7040/ 8040 or ipq807x platforms. The former only offering SBC like specialty devices, the later only having very basic OpenWrt target support at the moment (this will probably get traction in OpenWrt soon, but not yet). You are just a little too early for these.
If you are looking for ARMv7 device, there your options are plenty - in rough ascending price ranges, ipq40xx, ipq806x and mvebu (ARMADA 370/ 380). In terms of wireless support the two former are better, but when it comes to wired routing throughput, mvebu takes the lead. Here you need to make a decision, based on your current needs - and if you get along with a much cheaper ("old") mips based design (such as ath79 or mt7621), you can still save a lot of buck by going that route now and deferring a potential upgrade into the future, when you need it.
I think I will get back to my initial idea - Netgear R6220, especially as I hear from you its pretty OK choice and it covers or my needs.
https://openwrt.org/toh/netgear/netgear_r6220
The one I have found is described as: Netgear R6220-100PES.
Does anyone know if this suffix -100PES makes any difference to HW and OpenWRT support?
It's just a code for geographical region.