Well, part of the reason I don't really like Ace is how far-fetched she is. The “good kid” teenage bomb-maker. Not just bombs but her own special blend “Nitro 9” that she whipped up after being transplanted myseriously to an alien planet and getting a job working in a… was it a diner? I don't remember.
I just couldn't believe this character… and that's saying a lot considering how strange some of the Doctor's companions have been.
I realize they brought her in to add some needed muscle, much like Leela, for the Doctor, but it just didn't work for me, Leela I could believe.
With the Big Finish productions, (which, I admit, I gave up around #35 because they were pushing too many Eighth Doctor stories, and those weren't very good) I felt that they “fixed” a number of problems with the later companions and Doctors. Colin Baker never had better stories and he really shows what kind of Doctor he could have been, and companions like Mel and Peri were toned down and eliminated their annoying qualities. Likewise Davison was given much better stories.
For example, I loved Whispers of Terror, that was Peri's finest hour and we couldn't see her facets at all – and it's an interesting story because it could only have been told in audio. The Spectre of Lanyon Moor stands out in my mind as being somewhat of a retread, but a nice vehicle for Colin and Evelyn Smythe, who was a decent companion. My favorite of the “new” companions from the audio adventures.
Mel was vastly improved in the audio adventures, with nary a single “Oh come on Doc! That's the spirit, drink some carrot juice!” at the most obnoxious and shrill vocal level she could muster, but, in ranking them I stuck to TV episodes only.