I don't know how you could argue that the chevy small block was the best v8 ever made. Just because they made a bunch of them doesn't mean they're the greatest design out there. The only reason the aftermarket ever focused on them so much is because they're common. Heck, only reason I built one was because they're cheap and I didn't have to change motor mounts! Furthermore, I wouldn't say the longevity of a SBC is anything more than average or maybe a little above average. If you want to see a motor you can't kill, how about an olds 350 or a 318 mopar?
SBC's I think have several flaws. The timing cover design was an obvious attempt to save money. They're not a good design at all. The oil pans don't seal well to the front timing cover. The motor is a stock 23 degrees whereas much of the mopar stuff is stock 18 degrees from the factory (see how much its going to cost you to make a SBC into an 18 degree motor). The combustion chambers on most SBC motors are poor and the port design on the heads from the factory is really not that great (considering the exhaust has to make an 180 degree turn from the intake to get out of the head).
That said, the oiling design and valvetrain on the chevy's were pretty good, but to be honest, I think the smallblock mopars had a nicer valvetrain from the factory. The stamped GM stuff for SBC (rocker arms anyway, not to mention cam failures and timing chain problems in the late 70's) is pretty inconsistent. Stock ratio being a 1.5 and many of the factory pieces not measuring even close to that.
SBC for all intents and purposes is a cheap, decent motor. That's why they used it for so long. I wouldn't say its the greatest motor in existence, though.
My vote goes for the rocket 350!