namhaY (<)
Both have atomic control over their bodies, and both are able Telepaths. Ikaris has psionic and T.K. attacks, and Jonn has his far superior super strength, phasing and shape shifting abilities. IMO, i give Jonn the advantage but i am a bit of a D.C. fanboy.
Ikaris:
http://en.wikipedia.org/wiki/Ikaris
Martian Manhunter:
http://en.wikipedia.org/wiki/Martian_Manhunter
Ikaris:
http://en.wikipedia.org/wiki/Ikaris
Martian Manhunter:
http://en.wikipedia.org/wiki/Martian_Manhunter