My favourite cases would be quite difficult to put on to paper, since the majority of them were so good. My favourites though out of all of them would have to be Bridge to the Turnabout. Just one of my favourites, being the ending to the trilogy and the mystery behind the Feys, the gravy and so on. I do have two other favourites which aren't standing out as much, but they deserve mention: Turnabout Succession just for the fact that it's a simple court case, and Recipe for Turnabout for the dropping of pens and Xineohp. xD
I suppose I should mention Turnabout Samurai as well.
As for least favourites of cases, I don't really have one which stands out, but if I had to choose one, probably Turnabout Big Top just because it was boring to do. The ending was good, but nothing else stands out after that. I'm planning on playing through JFA again soon, and might just use AR to unlock all the cases just so I don't have to play that case again.