I just bought the ansem board and got ATK B IV max & GA II, Second Chance II, and ATK Boost III & Lux. 

https://imgur.com/a/7opel

The medals that I have guilted are Tifa and Aerith, Key art 8, Sora&Roxas, HD Axel, Xion, kh com mickey, Sora&Riku&Meow Wow, HD Aqua. What will be the best medal to put them on. I do have Hd Xion and Illustrated Terra B but both of them are only at 3 dots and I'm pretty sure they aren't gonna be guilted for a while. 

I would either put Second Chance II on Sora, Riku, and Meow Wow, or Tifa and Aerith, or HD Xion. For ATK Boost III & Lux, I would put that on HD Axel or Illustrated Terra B and same goes for the ATK B IV and GA II. 

Since the AB4 also has SP2 on it, I would honestly save that until we get a high-cost medal (like Xigbar B, or Xaldin B). Definitely don't put it on HD Xion, but if you ever guilt iTerraB, he might be a good candidate.

 

AB3Max+Lux is for whatever your best raid medal is, so preferably something that fits a high multiplier slot and is AOE all; Tifa and Aerith could MAYBE fit that, but they're better off early in the Keyblade, so maybe not. My vote out of your current medals would either be HD Axel or KA8, but there's no harm in saving things either.