I think it's because spike's new model is different but doesn't ruin it, like the Christian Bale batman movies (opinion, no offense). I like Spike in this pick, mainly. Although rainbow dash looks pretty bad@$$ in that pose, and I'm not her biggest fan, either.
And that's why she's not my fav. Oh, she's got her charm and doesn't always mean to be brash or arrogant, but she gets carried away in her over zealousy and arrogance, since her strengths are very noticable at face value (and her little fan club probably don't help. She should occasionally share the spot light with fluttershy to balance things out). Her attitude doesn't make her horrible, but as her friendship with Gilda shows, she's not too far from crossing the line into being a bully, if a minor one at that.
To be fair though, I never really hated her. I guess memories of some friends I had kind of set me off. People get so caught up in how SPC America they are, and after being a good friend and listening to them bitch about their problems (when you've gone through worst crap) they look down on you after helping them. They act like they're too good for you after you helped them. Rainbow Dash would think cuz she's the best, she's the only person that could complain about getting screwed cuz she's too good to let that happen. It's karma she never gets to be in the wonderbolts, because of how she ignores and looks down on scootaloo. It's like Haruhi. If she was my kid, I would love her, but I would fly up her ASS about what she did to the computer club. Then just stare at her in shock about what she did to the time traveler girl.