On another forum, I have received other recommendations for the Sierra Wireless cards. The Dell-branded units, while inexpensive, were not recommended to me there due to the complexities and reliability of re-flashing them to "vanilla".
Make sure whatever you pick supports the bands that your provider supports and has sufficient signal strength at your location on those bands.
Watch out with the Huawei in Hilink-mode ("h") models, rather than Stick-mode ("s") models. Only the Stick-mode units expose the interface directly; the Hilink models have internal NAT.