There's a small group of us in here who are huge fans of the 990v4. In terms of comfort and quality few other NB models currently compare. Also, 990v4's tend to be more affordable and can be had for cheap if you look in the right places. It's very much a grandpa shoe (I actually bought them for my pops who is indeed a grandfather) but if you're not afraid of that then I'd highly recommend starting there.
Probably the overwhelmingly popular models from the made in U.S.A. line are the 997 and 998. If you scroll through all the posts you'll see that there's a lot of debate about NB's recent quality control issues. Some of the best 997/998 shoes to have released in recent years (in terms of shape, quality control and color ways) are the earlier retros from a few years ago. But, honestly, the newer ones are still really solid and I think NB has dropped some really great color ways of the 997 this year (997CSU from 2017, 997BKR from late 2016 stand out to me).
The other really popular models come from the made in U.K. line - the 1500 is the fan favorite (and rightfully so). The 577 has historically gotten a lot of love while the 991 is also a cult favorite for a lot of us in here. In terms of quality control, shape and execution the U.K. factories are doing a better job in recent years than the U.S. factories.
Hope that helps. Stick around here, dudes regularly post links to sales and deals and such.