If your importing from pro tools you can just open a session in 48 then select import audio (shift command I) and select the track, and it will be converted. If it is a whole session, open the 44.1 session then go File-> save copy in, then select the sampling that you want the session converted to, 48k, just make sure that the audio files get copied over by checking the box (should be selected by default).
BarbaBatch is great, probably the best sounding option. Sound Grinder is a much cheaper alternative and sounds very good. Only a fraction less excellent than BB. ProTools import/export using TweakHead is hard to beat.