Any should do. It really depends on factors other than what you've listed. If the TV is wall mounted, for instance, you might want to choose a stick model. If for any reason a wired connection is preferred, go with the Ultra. If none of that matters, the Express is the cheapest option, although the Premiere is a slightly better (and slightly more expensive) version of that.
My go-to recommendation is a Stick+, as it's a good middle ground, and includes a remote that also controls the TV power and volume, making it easier to use (only needing a single remote). However, if the user will need to switch remotes anyway, or will use a universal remote that can control several devices, then don't go with the stick models, as the IR universal remotes don't support those. If universal remote capability is needed, I usually suggest going with the Premiere, particularly if it can be found on sale.
DBDukes http://www.dbdukes.com/Roku Ultra (4660) Roku Streambar (9102) Roku Streaming Stick+ (3810)