A couple of years back I really wanted a DPMS but after some research on sites such as lightfighter and M4carbine.net I changed my mind. Not that I need something to go fight wars with but being it was my first I wouldnt have to turn in to the armorer the desire for as close to top of the line as could be afforded was there. LWRC was the choice. If I were granted a do over KAC or BCM w/ some extras would be my choice. I also own a Spikes that has been nothing but a joy to shoot.
As of yesterday, I have 3 AR's. Two are complete CMMG and one is a Bushy upper on a CMMG lower. I'm not a "fanboy" by any means, but I do think that CMMG is every bit as good quality-wise as any other mid-range manufacturer. I've had no issues with any of my CMMG components.
So, I wouldn't hesitate to buy the CMMG. They are well made and so far they are 100% compatible with any upgrade or aftermarket part I've used.
DPMS aint bad but I'd say your first 2 options were a whole lot better. Spike's is a +1 on my end since I don't know to much about CMMG. Spike's has good customer service to boot and are reliable to the end. Just my .02 let us know what ya get.