Okay people, calm down. I will summarize all that has been said thus far:
-IC mains argue for a 70:30 IC. Reasons are the CG and the Ice Block gimp
-Ness mains argue for a 55:45 or 60:40 IC. Reasons are that ICs can punish anything with lag.
My input. The ice block gimp is situational due to the fact that you would have to force Ness into that position to get him to recover from there. Since IC lack an attack with good horizontal knockback, this isn't happening to often. The spike is also situational.
Ness can gimp them better using PKT. Hit one of the climbers before they recover (I think), and both will desync. Now desynced, they can't use Belay to recover and one of the climbers will end up dying.
In terms of spacing, Ness can space better than ICs by a margin. However, Ness doesn't want to be punished, so his approach game becomes a matter of fairs, and other aerial approaches. IC's have a projectile, the ice blocks, but they are very poor projectiles since you can knock them away with any attack. Again, Ness doesn't want to be punished, so he can't start a projectile spam contest unless he is far from punishing range.
Since Ness can space better than ICs, getting grabbed isn't easier for them. However, Ness could get grabbed in certain instances (like a desynced IC situation), so this has some effect in the matchup, but possibly no more than one should give it credit for.
All in all, it looks very slightly leaning towards climbers due to CG->death. However, one of them must first land the grab which isn't easier here. At this point I'd go for 55:45 IC.