I've dived on the east coast for about 2 months in june-july, it isn't as bad as those pictures make you think, that was probably during an anti-cyclone. Also dived 2 months on the south coast, and did some dives in the north and the west.
Don't worry to much about the weather (with exception of the South, don't go there around July). Rather think about what you want to see?
For me the South is fantastic! You get to see sharks (including bullsharks if you're lucky @ Pass St-Jacques), huge rays, colorfull fish and the divesites are fairly attractive, meaning there is nice coral with anemones and nudiebranches if you also like some smaller stuff.
The east isn't that good, divesites are nice, not great. Coral is ok, but you don't get to see lots of fish, small or big, still enough to be ok though.
The north is fantastic if you like alot of (small) colorfull fish, beautifull coral and always want to have a good vis. (+-30m since the north is protected from currents)
The west is a bit less then the north but still better then the south/east if you like small fishes and lots of colorfull coral.
If you like to dive on some wrecks the north and west are also the best startingplaces.
Hopes this helped a little!
Grtz, and dive S.A.F.E!