I'd recommend the corn snake as the best pet quality snake. I consider factors such as feeding, temperature, space, temperament, and attractiveness (many color and pattern varieties in corn snakes).
One largely ignored species that makes a good captive is the black milk snake. They are a bit jittery when their young, but totally calm as adults. They may grow larger than 5 feet, but make up for it by being TERRIFIC feeders, docile, and have lower temperature requirements (can thrive at temps of mid 70's w/o supplemental heating- they AVOID temps in the 80's and above) and slower metabolism. Imagine a very calm 6 foot black snake that needs to be fed only every 2-3 weeks (and never refuses this meal), can be kept in an enclosure smaller than most 6 foot snakes require, and poops once every couple weeks in compact logs with little odor. Very low maintenance, but an very impressive animal.
Black milks have exceeded 7 feet in length, but this is rare. Just over 5 feet would be average.