Hi,
Canaima / Angel Falls is definitely better in the wet season as you then can travel up the river by canoe (GREAT experience).
I'd suggest a trip to the Gran Sabana in dry season - it's the most marvellous scenery. I was there in wet season, so I got WET, why dry season probably is to prefer :-) You can hike Roraima (didn't do it though) or just explore the small villages, campamentos and fantastic tepuis between El Dorado and Santa Elena de Uairen.
Or try a canoe trip on Rio Caura including the Para Falls, we're going to do that in february, because Caura River has water enough all year round (e.g. check Gekko-Tours).
Of course I hear a lot good stuff about Merida in the Andes (haven't been there yet), where you can hike, paraglide, go with the Teleferico and a bunch of other things.
We're also going to Parque Nacional Henri Pittier in the North where there's a lot of small beaches, and I also heard good about the area of Morrocoy / Chichiriviche...
Don't know a thing about scuba diving :-)
Have a great trip!!!