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They work VERY differently. Offensive is meant to tear holes by its larger power and stay alive for a short while, while the Defensive is meant to steadly set-up on the opponent and then sweeping.
I dunno if I'll be playing Ubers, but I signed up for it. The other teams I have are old and pretty much crap ('cause I was testing stuff), so if you feel like giving me a few, let me know.