I use two lenses for 35,120 (6x6), and 4x5 use. Schneider Componon-S 80/4 for the two smaller sizes, and a Nikkor 135 for the bigger. I used to use a el-Nikkor 50 2.8 for 35 which was great, but the new-to-me 80 covers both.
There's so much stuff on the used market or being thrown in the dump with enlargers that didn't sell, theres no sense in dealing with no-name lenses unless you really want to. Rodenstock, El-Nikkor, Schneider, etc... are generally good and I'm sure others will have good favorites as well.
What's important to me:
1. A bright aperture is worth paying a little extra for. 1 stop makes a big difference in focusing. Not so many aperture choices in the longer lenses, but there is a lot of choice in 50mm range lenses. For now, I can get away without a focusing aid except when printing soft focus stuff. That may change in a decade or two.
2. Avoid dirty junk. Sometimes it can be cleaned up, but there's so much pristine used stuff, there is little sense to buy lenses the DPO didn't take care of and smeared them with dektol, acid, fixer, tobacco, and dirt.
3. consider ergonomics. I like lenses that click at each stop so I can know in the dark how stopped down it is. Other people like smooth aperture dials to work with darkroom metering methods. The scneider also has a lever to go wide open and the aperture setting is backlit. Nice but not critical.
For 4x5 I chose as wide a lens as practical for 4x5; 135 instead of 150-160 range. I figure that will give me a few inches bigger enlargement before the enlarger bumps the ceiling.
