For Flash I suggest the Mark Waid run. It's not Barry, but I feel like you will like Wally just as much, if not more if you do already prefer Barry.
For Supergirl I suggest Silver Age if you are into that sort of thing. You can also try reading Superman/Batman: Supergirl by Jeph Loeb which was the official return of Kara after almost 20 years after killing her off in COIE. Then you can read volume 5 of Supergirl which was her new solo series after Kara's return in Superman/Batman. The first 20-30 issues are mediocre at best, but as soon as you hit Gates' run you will get completely invested. I also might suggest reading the Peter David run. It's not Kara, instead it's Linda Danvers. The first, like, 20 issues are pretty good, but after that it's down hill from there. The Earth Angel BS is what really killed the run. I haven't read his run in full but I hear that Many Happy Returns was a great return for the book... Before it got cancelled immediately afterwards.
For most when people think of N52 Supergirl they think of the gates of hell opening up and dragging the human race into the burning abyss. Overexageration, I know, but regardless I actually like vol 6. Sure, I've read better, but I still like it, and you might too.
If you are into non-canon, severe origin changing books you might like Supergirl: Being Super, and while I liked the idea of it, the execution was awful imo.
Vol 7(the current run) will start of good, and by issue 10 you might notice a slip in quality, and after issue 20 you will probably get pissed off like a lot of Supergirl fans did for once again taking away character development, but hey, maybe you can still give it a shot.