If you can get it Phil go for Fresh bait,best to collect it yourself then you know its fresh.
i keep all my old shell fish bait in a tub and keep re-freezing it after each session,its minging and some is probably a few years old but its handy for bulking up baits and leaving a sent trail.
Other than Rag worm i try not to waste any bait.
I've never tried re-freezing crab as i was told it was useless once re-frozen however i'm sure it was mentioned on here that someone re-freezes there's