Best bet is to buy a refurbished machine from Apple. You save money, have the peace of mind that your Mac has been checked, and you get a warranty.
The link is the UK site, but the same applies in the states too.
I would really lily to try a Mac, either a Pro, Air, or Imac. Not sure which would be best. But, I would lime to try used to save a little money. oOr, Should I avoid used altogether?
macofalltrades.com, I've bought from them and they're very professional, located in Florida, and their inventory changes daily.
I don't work for them, I live in Kentucky