I have to say that those are two very nice cases and your going to have a tough time choosing between the two.
I like the HAF XM and I have the HAF-X so I can see some similar features in the XM the case is roomy and has good fan setups so you can add a lot of fans if needed.
The C-70 from Corsair is a new model just out and it looks good , the fan placement is also good and numerous. I don't know what you can get for a selection of models but in Newegg here there are four with the best one being the army green and it looks exactly like an ammo case and is pretty cool looking with the latches and all.
I don't know, I usually say that a case is more of a personal choice because your the one that has to look at it and as long as the air flow is good a case doesn't add much else. Both cases have excellent air flow capabilities.
I would have to go with the C70 if you can get the green one , if you can't then the XM.