How Good/Skilled are the TMNT?

I've been curious about this, because the turtles have fought aliens, robots, ninjas, demons, mystic forces, gangs, time travelers, and even dinosaurs. So how skilled/powerful are the turtles as indeviduals and as a team?

@opticblast98: I've never regarded the alien fighting cartoons to be very canon (maybe they are).

Physically they are superior to most humans due to their skin and shells. Martial arts wise they are on the top of the list. When they're not goofing around they can be very deadly (as seen against countless foot soldiers).

I've never understood why they can't take Shredder in a 4v1 fight though.

@frozenphoenix: well in the comics they have fought aliens like the Triceratons, utroms, and the federation. Oh and shredder I believe is probably on an entirely whole other level then the turtles maybe because of magic or experiments