I would say get both, but if you can only get one, go for Trails. While in my opinion, Shadow Complex is possibly the better game, I've played it once and beaten it and haven't touched it since (although several reasons to blame for that, mainly backlog). Trails on the other hand, is great for pick up and play action, and while I just bought it myself a few days ago, it feels to me that it could be a game I'll keep popping in from time to time either to make new tracks or for time trials.