*Dusts off account*
Hmm...an interesting question. While I have not seen that many Sentai* series, out of the ones I have seen...I would probably give the award to Alata.
Marvelous was set up to be a badass from episode one, while Alata was initially written to be more of a centering element to the team. Therefore, when I saw him do things like calming the Abare Headder and the whole battle with Dark GoseiKnight of the Groundion Headder I was just amazed. Deflecting laser blasts unchanged with your hand (and a box of scraps!) helps, too.
Another factor for me is the fact that Alata never gave up. Beside the former two incidents, an early example from the Warstar arc was the spin flip...thing. He did not give up in showing Nozomu that it was a useful technique.
Finally, mention must be given to the actors, both Yudai Chiba and Yasuhiro Takeuchi. Chiba, especially after the Warstar arc, gave the role of Alata the appearance of a person who loves the Earth. Outside of battle, this manifests as an obvious desire to experience as much of the culture as he can, and Chiba lets that come through excellently. Takeuchi shows Alata's determination in battle; his desire to fight as hard as he can to protect the planet. The way Takeuchi did the swordplay with the Skick Sword was far and away one of the more enjoyable parts of early Goseiger for me.
That's most of the reasons why I think Alata is the most badass Red out of the Sentais I've see more than half of. I probably missed something, but I think I covered most of my bases here.
*The list, for sake of comparison and everyone knowing my limits of Red knowledge are: Dekaranger, Magiranger, most of Boukenger, most of Gekiranger, Go-Onger, Shinkenger, Goseiger, and Gokaiger.