Buying advice b/w Cannondale Quick CX3 vs Specialized Crosstrail Sport Disk vs Disk

Please help me decide b/w the following. I was first going for the cheaper $579 Crosstrail disk, but the LBS person suggested looking at the ones with the suspension lock out. I'm trying to keep my budget reasonable. I'll be more of a Sunday rider with my son who I bought the Specialized Hotrock 24 21-speed bike
http://www.specialized.com/us/en/bc/...04&scname=Kids

I'm trying to find the best bang for buck b/w the following 3... the LBS rep suggested looking at hydraulic disks too but I think staying with regular disk brakes may be plenty for me. I'm trying to figure out at this price point, is there a major difference b/w cannondale vs specialized specs/quality and what I'll be getting for my $

Cannondale Quick CX3 $799
http://www.cannondale.com/2012-quick-cx-3-21063

Specialized Crosstrail Sport Disk $749
http://www.specialized.com/us/en/bc/...name=Multi+Use

Specialized Crosstrail Disk $579
http://www.specialized.com/us/en/bc/...name=Multi+Use

Thanks in advance