Personally I love that last diving Gannet shot, but then I'm a sucker for action photos!
I agree with what everyone has said about getting something that stands out, and is a bit different from the usual shots seen. Unusual behaviour or a tricky shot will always be judged favourably, especially if the shot is aesthetically pleasing as well.
Also try smaller local competitions to gauge what judges seem to like, possibly through your local camera club? The critique I've had through entering these has been so useful, and I've definitely improved massively since joining a couple of clubs.
This is probably my most successful shot to date (it's not one that I've managed to sell as yet, people seem to like my cutesy puffin ones as presents for relatives, plus it wouldn't be a valid entry for national competitions if I'd sold it) but I feel it ticks most of the boxes. Although it's of a very commonly photographed subject, you don't see many decent shots of Red Kites actually swooping at ground level, especially in such wintery conditions. Most are of them cruising past in the sky or eating food on the wing after they've picked it up.
For the record, it's won the regional photographic competition at work, and was also accepted in the Welsh Photographic Salon (it didn't scoop any of the prizes though, but I was happy to get that far quite frankly!). It's also been shortlisted for the BWPA, which I'm ecstatic about!
Good luck!