For a newbie/novice to building and tuning engines, and for a mildly built or stock street six cylinder I say go with a small (very small) 4 barrel or a 2 barrel. For best performance keep the 4 barrel at around 400 cfms and the 2 barrel no more than 350 cfms.
Twin one or two barrels would burn more efficiently I'm sure, as the carbs are set closer to the ends of the engine. And you'd probably get better throttle response and overall performance from 2 two barrels versus a single 4 barrel. But for maintenance and tuning purposes the small 4 barrel would be your best bet.
Either the Clifford or Offenhauser 4 barrel intakes will work fine. Unless you make your own they're your only two bolt-on choices for a street engine. You'll have to adapt water heat to the Offenhauser and the older Clifford intakes that don't have the water jacket built in. Unless you've done some extensive head work and have beefed up the cam I recommend the Offy, as the Clifford has larger intake runners for better upper RPM performance. The Offy should work best for low-mid RPM torque & HP. And from what I've seen over the last year or so the Offy generally goes for about $100 or so less on Ebay than the water heated Clifford 4 barrel intake.
-magic mike-
