I'd get a baby boa personally. They're generally very handleable, great eaters and look stunning. I've just bought one for my son's 13th birthday, and it's great as it'll grow with him.

Obviously though if you don't want a snake that will get big, then you'd be better off with a corn or a royal, both are great beginner snakes, although if you went for a royal you'd be wise to see it eating before taking it home. A reputable breeder/dealer will be more than happy with that.