For the bulk of my simming days I played a normal lifespan - this was because I didn't patch my game very far and I believe that adjustable life stages came with the Generations patch and I don't do babies and the toddler stage only needs to last until the toddlers have their main skills. I know I could have aged my sims up manually but I would have to do that for the whole town and that would be too much work. I find that I can get a lot accomplished in my sims' lives on the normal lifespan (with the Relativity mod of course) and was quite happy to play that way for many years. I also find longer lifespans dangerous for me because I can't help but let my sims have more babies whenever they wish for one. If they don't live long, they can't do that to me ;)
I took a couple of years off simming because of big life changes but when I came back a year and a half ago I decided to try long. I did enjoy it but found the wait between generations painfully long. I am a generational player so this was hard for me. It also meant my families were bigger and that meant more work finding partners for and setting up of spares.
My current save, which I am enjoying immensely, is on a modified medium lifespan. I toyed with the idea of short but it was too short because I didn't want to adjust pregnancy times because I like seeing my sims pregnant. My sims get just over 50 days (my elder stage has been lengthened because I didn't want to lose them too quickly) and I am flying through the generations and the town is ever changing because of the rapid turnover. For someone who plays for genetics, this is perfect.
I think I tried epic once in my early days of simming but it wasn't really my cup of tea.
