I would go for a little of both. A winning robot is great, but if isn't of very good quality and isn't reliable, then teams won't want you for finals. Pretty robots aren't going to get you far either. You're not going to waltz right into the finals only because your robot is powdercoated. You have got to show what you can do. If you can do a lot of things well but die every other match, you're not going to last very long. However, if you have robot that does one or two things really well and has very little problems, you are going to make it pretty far, and if your robot looks good doing it, it is an added bonus
. There are really two types of problems with robots - normal wear and tear and robots that do so much that they are too suceptible to damage. I have seen a few good looking robots where they have a lot of capabilities and can do a lot of great things by themselves but when you throw them on the field with some of the simpler robots, they just can't quite cut it and systems keep breaking all the time or have to remove subsystems because they are causing too many problems. This is where reliability and quality outweigh a robot that is built to do everything. Through my expirience in FIRST, a quality robot is a winning robot.
Eric