Redtail boas also get FIFTEEN FEET LONG which I think kind of disqualifies them as starter snakes. I've just seen way too many 8-10 ft long redtails CRAMMED into 40 gal aquariums because the owners didn't think about how big it got when they bought that cute little hatchling.
Best starter snake in my opinion - probably hands-down, ball python. King snakes and Corn Snakes are cool and very easy to care for - but they are also MUCH more active, so actually require more space than a ball, even though they are smaller.
If you want to spend a little more money and get something a little less common (since every 12 yr old kid in the world has a ball python), go for a hognose snake...very unique looking, lots of weird behavior and extremly easy to care for.
Or...you know...get a tegu..wait...thats not a snake.