Against Marth:
If you're off the ledge, you're dead if he reads you correctly. Ike has limited options of recovery, so this isn't too difficult. F-Air, or simply running into Quick Draw will beat you out, and possibly kill you.
Aether can be beaten out by Counter or Dolphin Slash. My friend, a Marth mainer will occasionally run OFF the stage with the counter to guarantee himself the KO.
Ike's advantages are on the stage, below Marth, and above Marth. On the stage, Ike has his jab combo. (**** canceling his jab. **** his **** with that third hit.) and all of his aerials. Correctly spaced, Ike should beat out most of Marths options on the ground. Below Marth, Ike has U-Tilt, U-Smash, N-Air, B-Air, and U Air. Below Marth, Ike has D-Air, and N-Air.