Sorry, but I think the original Red Dwarf is the best, but I enjoyed Better than life too. Wasn't impressed with "The Last Human" at all.
I've also read a book by Robert Lewellyn (Kryten) called "The man in the rubber mask" which is all about how he got involved with Red Dwarf and loads of interesting behind the scenes stuff. He's a seriously funny writer, I'd recommend it for any Dwarf fan.
'kay, I'll shutup now, promise.