Well, there are a lot of good choices and a lot of poor choices. Take a look at the FAQ here. It has lots of good info about different flute brands.
You didn't indicate if you are looking for a flute that is ready to play or whether you are looking for a fixer-upper to practice your flute repair skills. Either way, for both purposes, it's hard to go wrong with any Yamaha flute. I would stay away from any off brand flute because they can be inconsistent - some are awful, but others are not bad.
Are you apprenticing at the music store or did you go to one of the repair schools for instrument repair training?