The first seems smaller, I would suggest the second.
I wanted this one:
Ford Racing Mustang BOSS 302 Laguna Seca Front Splitter Kit M-16601-MBKITA (10-12 GT) - Free Shipping M-16601-MBKITA
But mine was free, and even if I paid for it, it would be worth the $200 for the looks and it's effect. I couldn't do a bigger spoiler for appearance, I considered a kammback, but the cost and work to make it look good for the lower gain wasn't really worth it to me.
I hope you know my front fascia, original lower grille block, upper grille, and air splitter ARE from Roush. Only my pre underbody air dam was home made, and it was edging, not coroplast. My coroplast is only upper gb, lower gb, and underbody.