Mayhem Missions, far and away the best part of Redside!
Seriously, check the Guides for how to get Lord Schnauzer as a contact, Mayhem Missions are some of the most fun you can have with your costume on!
I find low-level Villain mishes, fighting Snakes and such, to be a lot of fun after endless Outcasts and Skuls.
Have to confess, in the mid-range, where you start to feel like an aspiring lackey, is where I wander off. Radio and TV are a blast, though!