You might want to define what you mean by 'which does it best'. I assume that you mean more accurately.
I'm sure I'm not qualified to answer this question, and I _KNOW_ I'm no guru, but I do know I haven't read anything that would compell me to think that conversion is no better OR worse in Audition 3.0 than in Audition 1.0 in terms of accuracy.
Having said that, Audition 3.0 seems to have better workflow than 1.0 in that most processes are performed faster on my machine. So if the definition of better is based on speed, then 3.0 is better than 1.0. 3.0 had some enhancements in terms of basic workflow features (fewer keystroke types of features), but honestly I didn't feel that there was all that much core feature-wise in 3.0 that isn't also in 1.0, but I'm not a power user for sure.
Having further said the above, I find that Audition 3.0 is a tradeoff on my machine because it seems to be a real RAM hog. Slows down multi-tasking and causes frequent lockups on my machine.
In the end, because of all of the above combinations of considerations, I've personally opted to stick with Audition 1.0. If I had a bigger, newer machine, I'd probably go with 3.0.
Have no idea about other software packages, so cannot speak to those.