The thing about Gurren Lagaan is that if you just keep it to the pre-Teppelin phases where humanity hadn't harnessed Spiral Power in any organized way yet, That solves pretty much all the problems, leaving the characters only very slightly more powerful than Gundam pilots. (and slightly less powerful, if the pilots are post Universal Century mech pilots who have those wierd mildly magical Gundams)
I'm tempted to go with a fairly gay Shinji Ikari, though if people would rather stay more hetero, I suppose I'd go with Nozomu Itoshiki, the suicidal main character from Sayonara Zetsubou Sensei. He's a schoolteacher who desperately wants to die, usually for stupid reasons. He has an uncanny ability to escape anything that could possibly kill him, which is good, because he teaches a class of psychotically insane obsessive schoolgirls.
As for Shinji, I see the character as bisexual, but leaning slightly towards boys. He covets women, due to his violent seperation from his mother, but he doesn't actually have the spine to go after them. Naturally, being so passive, Shinji makes a great patsy or sub, but he doesn't STAY compliant.