what is the best small block and why ?

HOWEVER - If i was building a streeter - I'd opt for the 360. More torque due to stroke and CUI, cheaper parts, and it will make power where you can use it.

A lot is made of the bigger mains on the 360 and the greater inertial friction - but I reckon the cui and storke of the 360 outweighs any minor disadvantage of larger mains.

Yeah but a high stall converter solves the low speed drawback of the 340. A 10 inch works great on the street and a 8 inch with a 4,000 stall and 4.10 gears would surprise many 360--408's