If this is your first snake start researching Corn Snakes, they are pretty well the best first time keepers snake. I would rule out Carpet Pythons, they can be tricky as young snakes and aggressive, plus their size can be harder to house. Kingsnake goes right with Corn as well. As long as you get from a trusted breeder like www.bhbreptiles.com you will have no problems with it. It will further come down to looks. What attracts you to the snakes. . . there are a LOT of color variations quite cheap when you look into Corn Snakes, there are also morphs that are fairly expensive (think in the upper hundreds to thousand mark in regards to scaleless corns). With Kingsnakes there are a decent amount of pattern variation, but not as much as the Corns. Kings can get slightly larger in bulk and length, but I'd still recommend going with what snake color theme fits your lifestyle.

Cheers