I'm a switch. That's right, they exist.
When I came on the scene in Summer 2009, I already knew I was switch, but (as many people do) started off pretty much exclusively sub, for various reasons. these were things like I wanted to put myself in the hands of someone more experiences to 'learn the trade' off of, and also, much more importantly, I didn't trust myself with anything I was doing, the closest I'd gotten to BDSM before was tying up a girlfriend with bondage tape when I was Vanilla.
After a little while I became a bit more confident, started topping a bit, became more adept and better at what I did, and as I became better and more confident, I realised that I really did enjoy topping and being dominant. At first I thought maybe I was going to become exclusively dominant, but all it took was a quick play session with me as the sub to realise that this was definitely not the case.
There are both good things and bad things about being a switch. It means that if you hit it off with someone you are that much more likely to be able to play regardless of their role, if they're bottom you can top, if they're top you can bottom to them, and if they're switch, that's where the real fun begins!
however it's when relationships get a bit more serious that it can get problematic. if a switch was going out with a top then he would bottom to her, but unless they were polyamorous he would have no way of topping anyone, as obviously his top partner wouldn't allow him to top her, and even if she did it could ruin the dynamic.
as it stands, at the moment I'm predominantly top, for the last 8 months or so I have done very little subbing and almost exclusively topping, in fact the submissive play has happened on 2 occasions with the same person, though this is more lack of availability with other people than an actual want to only submit to one person.
The way I've described switching to people before is through taste. it's the difference between liking the taste of chocolate/sweets and liking the taste of wine/beer/alcohol. they both taste great, but they're completely different tastes, and they give you different feelings, different emotions, different highs...
I would have to say that, despite hardly ever doing it, my first love is still to bottom. I love topping and being a dom, especially as I seem to have gotten far more hot girls that want to submit than hot girls that want to top me[FAO girls that have topped me: you are also all hot, there are just less of you in number than girls I've topped], but being the one that's hurt, the one that's fucked, the one that's played with... it just takes me to a different level.