I don't think there's any FF you should just skip, especially once you play a lot of them. At least for me it was really cool to see the evolution of the series and I think almost all of them have something to offer players. Obviously there are ones that should probably be played after you get through some of the better ones, though. FF1-3 haven't aged the best, but that's to be expected, really. They're not bad, though.
Personally my FF rankings go:
1. FF7
2. FF8
3. FF9
4. FF11
5. FF6
6. FF12
7. FF13
8. FF10
9. FF4
10. FF5
11. FF15 (30 hours in)
12. FF2
13. FF3
14. FF1