Most people prefer Kururu because her relationship with Ikki has to become deeper than love itself, plus she is the only girl who is currently there for him.
I'm still a Ikki/Simca fan though! If they don't become a item, (which looks like the case) OH! GREAT! should give us a damn good Ikki/Simca moment/conversation where they only talk about them w/o interruption. (but thats just me)