Like all other have said... very personal thing. FWIW, I am 5'10 with 30" inseam. I ride 90mm stem, but that's only after I have experimented with different combination of stem length *AND* saddle fore-aft position *AND* crank length do i arrive at my current set up. So, just stem alone does not determine the best fit, but it's one variable you can experiment with.