It depends. (The correct answer to most questions.)
You should buy based on traits, not appearance. Just like when you judge people.
Best snake pets, in order, and why. Your priorities may vary. Here are my choices:
Kingsnakes
Good feeders, eat a wide variety of prey, some individuals can be very spirited and are generally more active than other Colubrids. Remain under 5 feet usually. Trade-off: Some subspecies have become VERY inbred. Breeding for color or anomaly produces a lackluster specimen. Some Cal Kings have been known to attack rocks and water dishes! My Labrynth was so sloppy striking that I traded him after a month. (I recommend Sonoran Blacks for two reasons: voracious appetites and only recently captive-bred.)
African House Snakes
Nothing strikes faster! They feed on a wide variety of prey. They only grow to 3-4 feet, come in a wide variety of colors, and feed and breed readily, year-round. Trade-off: They remain very slim, not full-bodied. More easily lost.
Corn Snakes
Handle very well and usually feed well, but have become VERY inbred. Breeding for color or anomaly produces a lackluster specimen that is little more than a gem that seldom moves. (The only one I ever had developed a fondness for defecating while climbing curtains. I have enjoyed all my Kingsnakes more; they seem to have more character.)