I find that it depends greatly on the weather. If it's below 40 degree's, the small block is easier. It stays at a more consistent temp. There's less surface area, so it doesn't cool off as fast. I always have a hard time keeping my BB's at the proper temp when it's cold out.
When it's above 50F, my BB's are easier to tune it seems.
Like rossb said, the BB's seem to be more forgiving since you have more power than a SB.
For SB's, I've had TRX2.5, TRX2.5R, Orion Wasp 18, OS 15 cv-r(X), Mach 15, OS 18 cv-r(x) and OS 18TM.
For BB's, I've had OS 21 RG's, Omega 21 comp, SH 28 and Axial 28.
Out of the SB engines, the OS 15 cv-r and OS 18 cv-r were the easiest to tune and held a tune the best.
Out of the BB engines, the OS 21 RG was/is the easiest to tune. The Omega was impossible until I modified an OS 21 RG carb to fit it, but it was short lived due to the fact that I milled down the carb neck and it cracked. Both the SH 28 and Axial 28 seem to have a dead spot at about 1/2 throttle. The Axial only has about 3/4 of a gallon through it, the SH was bought used and I've put about a gallon through it. They both run well, just have a dead spot.
