This is a topic I've been interested in for years now. As I don't get to see alot of others work in person, i'm always intrigued by answers to this subject.
I mostly print on 8x10 and 11x14 paper. I shoot 6x4.5 and 6x6, so I print 9x12" on 11x14 and 10x10" on 11x14 for the 6x6 work. I recently did my first solo show and printed 16x20 prints for the first time in my life. WOW!!! I was blown away by the amazing detail in the prints. I did 4 of them for the show, 3 were printed 13 1/2 x 18" (6x4.5 negs) and one was 14x14" (6x6 neg). I haven't printed since I printed these and it's left me wondering if my time should be better spent only printing 11x14 and 16x20 in the darkroom. The amount of time spent in the darkroom whether it's 8x10 or 16x20 paper is the same. The feeling and impression I got from these large prints blew me away and I think opened my eyes to what kind of potential my negatives really have. I will certainly be printing more 16x20 in the near future.
However, there is something to be said for the small print. Every photograph is different and demands its own size. I've printed holga images at 7x7" that sing, but when enlarged to 10x10" lose all impact. Photography is funny like that and alot of times you'll figure out how large an image should be printed simply by printing it one size too big.