So when you talk about most badass Reds, you need to define what qualities you consider badass. For some posters it's clearly presence or ability to tank through a serious beating, which are eminently respectable metrics. That's not where my mind goes first, though.
For me, I would say it lies in the question, "If you as a hypothetical bad guy got into a fight with this Red, how badly would you be fucked up before your inevitable defeat?" I mean not just beaten, but thoroughly owned, wrecked, and ruined so badly that you're praying for death before it comes.
I mean, let's face it, any Red is going to beat the bad guy and save the day. That's what it means to be a Red. But which Red is such a badass that he wouldn't just win, but absolutely **** your **** up? For me, the answer is clear: Ryuuranger. This guy has a proven ability to not just beat, but seriously **** up bad guys even before he even transforms.
And then he gets more powerful!! He flies around on a robot dragon and spews fire and gets a bunch of extra weapons! He gets a gun that shoots lasers on top of knowing mega-sweet kung fu. Holy ****, I would never mess with this guy if I was a rubber suit monster. I would go rogue and fight Gorma first, they're actually less likely to completely wreck my ****.