http://www.lorenzini.com/jlorenzi/encoder.html
My comp's having a hell of a time finding the page, so it may be either temporarily or currently down, but either on this page or linked off it is a test these guys did, using some sort of analysis software to measure the sonic degradation a number of different encoders imparted on a sound clip. They concluded that below 128kbs Fraunhofer is ptobably your best bet, but over it Lame takes precidence, and that Lame @256kbs was the most accurate encoding rate of any of the four or so encoders they tried, even surpassing its own performance at higher bitrates.
I post over at
www.guitarwar.com and usually encode in both goldwave and tob fantastic, and A/B the versions. Rob's usually better at low bitrates than goldwave armed with the lame.dll plugin, but sometimes the way lame distorts a sound at lower settings actually works better with the particular tune than the way the fraunhofer does.
Mp3.com's decision to allow premium members to upload 192kbs mp3's is stupid- fraunhofer doesn't go that high, i believe, and sounds increasingly harsh at higher bitrates anyway if it does, and the difference between a lame-encoded mp3 @ 128 and 192 is negligable- it's a marketing gimick, essentially, and a pretty bad one at that. From their perspective, it makes even less sense- they're allowing people to upload mp3's that are 50% larger than "standard" 128kbs. switching to 256k would only take 25% more storage space, and would actually give a notable increase in sound quality- there's MUCH less distortion to the high end, particularly audible on the cymbols. I've got a pretty good ear for this stuff, and even I wouldn't want to try to discern .wav from 256kbs mp3 with anything important on the line- you get faint high end distortion and what sounds like a slight narrowing of the stereo spectrum, but we're talking subtle, easily within the "am i imagining this?" limits.
Mp3PRO has a lot of potential as a low-bitrate mp3 encoder, but by the time you get up to 80kbs or so, the difference between a mp3pro mp3 and a regular one begins to fall off substantially. Below that threshold, the mp3pro sounds like it's approximately double the bitrate it is. Above it, it gets less and less noticeable, until by 128kbs there's very little real difference. If the codec ever becomes widely available as a decoder (winamp 2.x didn't have it stock, but there were downloadable plugins for it last i checked- i've got one if you need it, for decoding but not encoding. Encoders, i don't think, never made it to shareware or freeware. I believe there's no native support from winamp 3.x either, but probably a plugin if you're willing to take the time to download it. Problem is, most casual users won't) then it would definately be worth pursuing, if you do a lot of lo-fi work. However, for high-fidelity mp3 encoding (no laughs, please

), lame is still probably the best bet.
Moral of this post, for anyone too lazy to read it? lame.dll @ 256kbs stereo.
-D