Few notes about Mikoto:
66A seems pretty worthless
66B is good (I follow 6SP+C with it)
66C is good for comboing into
6SP sucks, it's slow and if you're not at least half screen away, you'll get hit in recovery even if it connects.
6SP+C is really good. I use it as a combo finisher.
Mikoto seems to play a lot like 3S Chun Li. Game plan is to poke with 2C, and hit confirm into 4SP+C super.
There is no training mode, so I have no idea how solid any of my combos are. Typically though,I'll poke with 2A and cancel into B's and CCC, then SP (usually 4 and 6 but sometimes I get 2 by mistake)
I haven't figured out a good Anti-Air or Launcher yet. However in air she can go A, B, 2C, Jump Cancel C, land, 2C, 4SP+C
PS. 664 dashing sucks.