The question is sort of vague. Obviously most people play through the actual game with a purely offensive team; what point is there in doing otherwise when you're not battling competitively? It'd just take too long, and wouldn't be worth it at all.
That said, when it comes to competitive battling, I prefer a little bit of both. I also dislike pokemon like shuckle, since people can switch in on him and set up, so he's not that great. Blissey is a very defensive pokemon, but I've seen her manage to sweep four or more pokemon in a row because she's so difficult to take down, and has a move like seismic toss which is reliable damage all the time.
Battling with purely defensive teams can go okay, but usually if anything goes wrong it's not good. It's always good to mix defensive and offensive together; a well built team with both offensive and defensive pokemon will most likely be able to take out a team that's purely offensive. There are different strategies, though... so for a doubles hail team I'm making, there's a surprising amount of defensive pokemon on it; mainly because stalling is something that hail teams do fantastically. :)