Totally personal chioce I think.... If you buy a hatchy you grow up with it... Become really fond of it and learn its traits, know by how it moves and acts when its in a bad mood etc.
If you were to buy a yearling, you will be unsure of it and of course it will be unsure of you.... Not that I have been really tagged by a yearling yet (touch wood), I am sure it will hurt a bit more than a new hatchy...
I say you get a Lil hatchy.... Just keep asking your questions...The more you learn the better off you snake will be when you get him or her...