When I first started doing grappling stuff with mates, before I had any training, I'd almost always attempt tp play guard just because I had the very basic understanding of how to get an armbar from the bottom and I was flexible enough to get a gogoplata. Granted I very rarely had good positioning, and it wouldn't have worked if my friends had been trained but I always used to go from the back.
When I started training properly I immediately found that I was more comfortable on top, crucifix, knee on neck and stuff like that took to me a lot more because I found I was able to wear people down and spend less time panicking about if i was going to get caught in a scarfhold, or getting tapped out.
I can do okay on my back but I'm always looking to bridge and get back on top.