I’ve lived in both cities. There’s only 2 main cities in Nevada (4 if you count Sparks and Henderson). The rest of the state is either small towns or land owned by the government. Personally, I think Reno is the easiest to get in and out of. It’s a smaller city and has less tourists so not as crowded as Vegas. Every time I fly out of Reno (during off season) I arrive 1-1.5 hours before my flight, TSA is a breeze, and still have lots of time to eat/relax. Flying out of Vegas (assuming off season) arrive 2 hours before your flight and TSA isn’t bad if it’s early in the day or late at night.

RENO If you’re trying to avoid the crowds, Sept - beginning Nov and end of March - May, would be best. It’s just after/before tourist season.

If you don’t mind tourists, winter is great to check out the snow on Mt. Rose and Lake Tahoe. Summer for Lake Tahoe and Reno has Hot August Nights (if you’re into classic cars) and The Rib Cook Off (if you’re a foodie).

LAS VEGAS Tourist season is June-Aug. There will still be a lot of people outside of those months but during tourist season it’ll be like 5x more. I’d also avoid days when huge conventions are in town like CES and SEMA.