Well let's analyse it shall we?
FF1 didn't really have a "Main character" but rather a few job'd fellows, so that can be disregarded
FF2 had Firion, who as you can see here [http://thelifestream.net/wp-content/uploads/dissidia_artwork_firion.png] does not have spiky hair.
FF3 we could argue has Luneth as the main character, who also does not have spiky hair [http://www.universoff.es/FF3/imagenes/Luneth.jpg].
FF4 had Cecil. Again, not spiky hair. [http://i243.photobucket.com/albums/ff226/jaken92/final%20fantasy/HeroDFinalFantasyIVHeroCecilHarvey.jpg]
FF5 has Bartz, who has sort of spiky hair, I guess? [http://media.photobucket.com/image/bartz%20ff5/oscura_belleza/games/ButzKlauser.png]
FF6 had Terra, who has boobies, but not spiky hair. [http://thumbs2.modthesims.info/img/9/0/5/7/3/1/MTS2_laaaaaaaa_1042333_Terra-ref.jpg]
FF7 has Cloud. Spiky hair.
FF8 has Squall, who sort of has spiky hair but it's all brushed downwards rather than gravity defying. [http://www.justadventure.com/articles/Squaresoft/squall.jpg]
FF9 has Zidane, Not really spiked at all. [http://ff.munkyisland.com/images/ff9/zidane5.jpg]
FF10 has Tidus. Fairly spiky hair, but not as gravity defying. Also one of the few characters who might feasibly use a crapload of hair product since he is a celebrity of sorts. [http://images.mylot.com/userImages/images/postphotos/2149782.jpg]
FF10-2 has Yuna, who has boobies, but not really spiky hair. [http://www.gaminggauge.com/wp-content/uploads/2010/06/ffx2yuna2ig.jpg]
FF12 was more debatable since although you played as Vaan, Ashe was really more of the main character than you were, and Balthier kept insisting that *he* was the main character. For argument's sake though, Vaan doesn't really have spiky hair that much. [http://www.ffinsider.net/final-fantasy-12/pix/vaan.jpg] He does have a stupid jacket though.
FF13 falls into the same trap as FF12 in that the story isn't directly about Lightning. Vanille, Snow and Lightning probably have the biggest "claim" to Main Character status but Fang, Hope and Chocofro are still fairly important too. Since Lightning's on the front cover though, we'll use her. She has boobies, and sort of spiky hair. [http://lcc.gatech.edu/~cpearce3/lcc4725/blog/wp-content/uploads/2010/03/lightning-final-fantasy-13-ffxiii-high-def-render.jpg]
So...yeah, looking at that, the non-spiky clearly outweigh the spiky.