S-force Megas zorb VS Arc-Gurren Lagan
The first scenario I would definitely have to give to Megas. Why??? Because he usually always has some kind of secret weapon that helps him win the battle. Megas has fought and won against enemies many times larger and more powerful than Gurren-Lagann, especially if it's just base form Gurren-Lagann.
You know what watch this http://www.youtube.com/watch?v=NvOl45W7EWE&list=HL1328828081&feature=mh_lolz
Also Megas would probably have a button that just said "Anti-Gurren Lagann missile".
This isn't really a competition at all, unless you used Tengen Toppa Gurren Lagann, then we might have a match on our hands.
Edit: http://www.youtube.com/watch?v=kaobllp9154&feature=related this actually shows you most of his weapons. See how he has a 5 minutes till the end of the episode of button and pretty much every other hax button you could ever want. Megas's powers are pretty much limited to Coop's imagination and if you've seen the show he has quite a big imagination.