Reletively new here but have been maining Ike since the beginning. What I've notice from you guys' suggestion for a good character partner with Ike, most of you've said High/S/A tier characters but what it really comes down to is asking your partner beforehand, how he plans to use his character during play in correlation to you and his targets. Coming from personal experience, I'd have to say Fox is highly compatable as a parter for Ike. Fox's abilty to rack up combos while Ike distracts them with brute force is absolutly amazing to watch. A fun little trick me and my Fox friend (can be done with anyone) learned is: once damage is about 60, grab the target and have Ike charge Eruption on either side. Plan your timeing, throw said target at Ike and watch the fireworks.
So it's really how you communicate with the partner. I would recommend someone with weak but fast building combos (Fox seems best here, but others such as Sonic, Squirtle, etc. work aswell) to compensate for Ike's slowness while he makes most of the finishing kills.