Ben Z
Veteran
I've had many different 90's, and my experience is if the lens has good glass and coatings and is properly collimated and hasn't been damaged (including tinkered with by an incompetent) you really can't go far wrong with any of them. Older lenses have somewhat less contrast and more propensity to flare with in-your-face light sources (making hoods desireable), and corner sharpness is down a notch until middle apertures.
The biggest advantages and disadvantages for me come down to speed and size/weight.
Currently I have 4 90's: a late (1956) LTM rigid Elmar, fat and thin Tele-Elmarits, and pre-APO/ASPH e55 Summicron. My favorite is the Summicron, but when traveling I opt for the small, light weight thin T-E. I have owned the last version Elmarit-M (great lens but not that much smaller or lighter than the Summicron, equal performance from f/2.8-4 except in the close range where the Elmarit-M wins by a stop), and the Voitlander APO-Lanthar f/3.5. The latter is by far the most modern-performing 90 you can get for screwmount if that is a criterion. Add an M adapter and it has IMO the best price-to-performance ratio of all, albeit it's not very fast. That was more of an issue back when I was shooting ISO 25-100 slide film (and why I sold it at the time) than it is now with digital.
The biggest advantages and disadvantages for me come down to speed and size/weight.
Currently I have 4 90's: a late (1956) LTM rigid Elmar, fat and thin Tele-Elmarits, and pre-APO/ASPH e55 Summicron. My favorite is the Summicron, but when traveling I opt for the small, light weight thin T-E. I have owned the last version Elmarit-M (great lens but not that much smaller or lighter than the Summicron, equal performance from f/2.8-4 except in the close range where the Elmarit-M wins by a stop), and the Voitlander APO-Lanthar f/3.5. The latter is by far the most modern-performing 90 you can get for screwmount if that is a criterion. Add an M adapter and it has IMO the best price-to-performance ratio of all, albeit it's not very fast. That was more of an issue back when I was shooting ISO 25-100 slide film (and why I sold it at the time) than it is now with digital.