We've fed live and are just recently going to try and switch them over to F/T. We are pretty sure the rats we bought were offered to another snake before we purchased them and transferred mites to ours. Most pet stores offer a return for store credit deal and you may come in and buy a rat that was offered to a snake with mites within the last few hours, bring it home and infect your own collection. Its safer to buy F/T in that sense. As for nutritional value, I don't think there's that much of a difference. Keep in mind though, that ALL food when frozen loses SOME nutritional value over time, and most people don't recommend keeping frozen feeders for much longer than 6 - 9 months.

Hope this helps.