If Luna wins this, but then loses to Rainbow Dash, I'm going to scream. We all know AJ's the toughest pony in Equestria. That said, Luna's got more magic power than a legion of Celestias. My vote's to Luna, but just barely.
Both are my favorites, AJ for ponies, and Luna for Alicorns. Argh, this is a tough one. Luna has beat all her opponents by huge margins, while AJ has barely scrapped the barrel each round. While I want to lean toward AJ, I think Luna has best chances of winning against Octavia & Fluttershy in the 4th(?final?) round.
My VOTE goes to LUNA , she's been on a roll since the 1st round and leads over AJ (45-27) with my vote.