SOUTH PHILLY. One of many places billed as Philly's "Best," Geno's certainly has its fair share of devotees on the south side of town. Begun in 1966 by fella named Joe Vento, this 24/7, take-out-only joint has the art of serving cheesesteaks down to a science. That is to say, at the first window, order your sandwich. Without prompting, indicate American, provolone or Cheese Whiz and whether or not you want onions. Pay, pick up your order, and move down to the next window for a drink. And just in case you're curious, you really shouldn't leave town without trying the Cheese Whiz variety.