I never had a 101 but have heard plenty of them. I always felt the audio on the 520 was better...at least I liked it better anyway. Audio is a pretty subjective thing to classify.
The 520 I had was great, very clean. I bought it off of a ham that just had it completely worked over, tuned, aligned, etc. When he sold it to me, he gave me all the paperwork, including the work orders. It cost him a pretty penny to get the thing operating how it was.
Long story short, when 520s are operating properly they are hard to beat. We all have radios that we wish we would have kept. The 520 I had is one of those radios. In fact, I really can't think of another. I say give the 101 a shot, but hang on to a 520, especially if it is doing well for you.