better drivability - Could be the SU's, but properly jetted Webers work great. Problem is getting them jetted correctly.
easier to tune - Some say SU, but I find Webers easy to tune if you know what you are doing. But for novices, SU's are probably easier.
cheaper - Used Triples with manifold probably $800.00 USD.
Triple SU setup probably $500-800 USD. I'm guessing, so ask Preston Pratt for a more definite answer.
and over all just better - Well here's where my bias comes in. I've been a Weber guy all my life. Ran them on VW, Porsche, and now Datsun. I'm quite comftorable with them, and they are infinitely adjustable. Different choke sizes, jets and so forth make them very tuneable. But, that can also be a downside, since you need to know what you are doing, or you can waste a lot of time and money trying to get them just right.