I find you have to be a little flexible. Not everyone is going to have everything going for him (control, splits, pitch quality, GB, velocity), but I tried to have a good mix and minimize the weak spots.
My current staff has:
-- 11 of 12 pitchers with control of 79 or better
-- 9 of 12 pitchers with both vL and vR over 60 (the others have vL or 59, 59 and 55)
-- 12 of 12 pitchers with P1 over 70, 7 of 12 with P2 over 70
I also tried to get rid of pitchers who were soft-tossers, so 9 of 12 now have VE of 75 or better. That adds to the Ks, and can make up for some deficiencies. Nine of 12 pitchers have a GB of 60 or better, which also helps.