what is the best small block and why ?

I like the 340 (building mine for my 70 Duster) but if you just want a car with more balls to it, I'd look for a late 80's/early 90's 360 (pre mag motors) that all ready have the Roller cam in them (I would have gone this route if 1. I knew about them at the time and 2. because I paid $50 for my 340 motor).