It's best to not talk about Robot Arena 1 as it's not very good. However, Robot Arena 2 is much better as it allows you to actually make whatever robot style you want instead of just having preset slots, which lets it have a long-lasting (13 years!) community of dedicated builders, even as so far to making 2 total conversion mods. However, Robot Arena 2 was REALLY glitchy, which is why now Robot Arena 3 is being heavily anticipated by the community.Polygonal!
I've never actually heard of Robot Arena 1, 2 OR 3!