I only started getting into the Big Finish audios last year, and they have a MASSIVE library, so there's still a lot for me to go through.
I'm currently going through the Monthly Range (which is still 275 releases!) and have listened to about 60 of them.
My favourites so far are:
* The Fearmonger
* The Marian Conspiracy
* The Holy Terror
* The Chimes of Midnight
* Spare Parts
* Jubliee
* The Kingmaker
* Red
I think most of the ones I listened to are pretty good and there's some very imaginative stories. Some are more middling and average than others, but I can still tolerate them (except Nekromanteia, that one is just pure dumpster fire).