If you don't have the equipment to take advantage of the lossless formats, you won't benefit from it. If you're happy with the way MP3 sounds, stick with MP3. Register to an audiophile forums and the things they'll say to you is "Welcome. Sorry about your wallet". Lol.
.wav and .mp3 for me. pretty much from what everyone has mentioned, .wav for the quality and .mp3 for the availibility and little HDD space.