FLAC, WAV, APE, DSD are always safer than mp3 if you aim for maximum sound quality.
Keep in mind you need real lossless files from good origin.
(mp3 transcoded to look like flac, won't sound like the real thing)
HDTracks is a nice place to get various recordings.
Some great recordings I have come from Sound Liaison, Chesky, Reference Recordings, LINN, 2L, Telarc, FIM, Stockfish Records, Naxos...
You won't find many top class recordings for very popular genres, more often than not all these audiophile labels make classical, jazz, vocal, acustic, you know...