[LAU] What is the best MP3 encoder?

Hi, I do have what I consider as a big problem with MP3 encoding, and that is artifacts and degenerated sound quality. End results are things like stronger esses, more "noise" (IE. something like schhhhhh upper overtones on disted guitars) and a loss of clarity. The thing is that a finished 320 kbps MP3 should not sound (significant) different than an original wave file IMO. Note that this artifacts are usually quite subtle, but very audible for the person(s) that recorded it and the mixer. I usually do mixes in 24/44.1 and I'm using dithering when exporting to a 16-bit stereo file. The artifacts, especially stronger esses are more audible without dithering and it should really not matter. I'm using Mixbus (Ardour) for exporting the wav files to 16-bit waves and Audacity for converting the file to a MP3. If I upload a lossless file to soundcloud, then the same problem comes there when Soundcloud converts it to it's player. Unfortunately, I don't have a raw 24/44.1 file and a MP3 I legally can post right now. But I hope that someone have suggestions about how to make the best possible MP3 files from a wave file. :-) Thanks, Jostein