I usually mix it up. I think I'm pretty defensive oriented, but that's mostly because I try every character even if I don't know much about them, so I prefer to punish the enemy for their mistakes when I'm playing someone I don't know much yet. Also since I main Scorpion and Sub-Zero for now I don't like being TOO offensive with him because any mistake is potentially a free combo for the other guy.
But like I said, I like to mix it up alot. When I play Kitana I'm extremely offensive, switching between long range throwing and short range special moves/combo's.
I was playing against this one guy today and I went through all my favorite characters but was still having alot of fun, so instead of being a douchebag and picking the same character again I just set it to random select. I got Johnny Cage like 3 times in a row. I actually think I could really start to like his playstyle, but anyway, I was being very offensive with him (I think that's how he's supposed to be played, anyway). Whenever the other guy started to zone me from long range I switched between throwing the green ball thingies and dash-blocking forward to get back to him. That seemed to work well since he never knew what to expect.
Next he picked Cyrax and my random selector also picked Cyrax for me. I'd never played with Cyrax before, so I thought I was going to lose, but a quick look at the specials screen and just mashing some buttons to see what he does later I was completely owning him. I love his net and bombs, seriously! In this case, I was using tricks alot
Oh and I played a bit with Ermac too. I like to mix it up between being offensive and zoning with him, people don't usually expect me to bring the fight to them when I'm playing Ermac.
So yeah... I guess I'm pretty adaptive. I'll see how I play when I find a favorite character...
Edit: added in some paragraphs for ease of reading.