I ride Western, and have rode a few years of English (though I doubt I could do so well anymore over those jumps, haha!). Thanks to the training from English riding, I feel I'm more balanced and composed on my Western saddle, but if a horse is bumpy at all I instantly post out of habit. Makes the ride smooth, and the horses never have complained. I started Western, and didn't even know English existed until I was about nine years old when I started. I have entered only one show, four classes. I gained a fifth, two sixth places, and forgot my final course so I didn't place at all. I was proud of myself.
I have since done a few fun shows with my old mare before she passed. We always placed in it, though we sucked at Western Pleasure. I'm a strong right handed person, so the whole "do it with your left hand" just peeved me.
I'm thinking about showing in something simple with my girl when she's a little older, but I'm not sure what. I don't know how to do much, so I'll probably pick halter so I don't have to relearn any balance or try to pick up a skill without an instructor. ;]