If you can afford it, I would go new. Just like an above poster said, you don't have to worry about things nearly as much.
I have all used kegs simply because I don't have the money for it - I have over 100 kegs, so buying new was not in the cards. I do have to be careful with certain kegs, and for some I have to add pressure to ensure a seal, check poppets, replace gaskets, etc. It is worth it for me to buy used and recondition the keg myself because I have so many.
If you only expect to have the one keg, or two, and can afford new kegs, you will keep yourself from having the same concerns as the rest of us who have used kegs. Just make sure you plan on holding on to those kegs, because if you decide to ever sell, you will then be selling used kegs, and won't get near what you paid for them originally.