I think that's gonna be a listener preference decision. Both are very good speakers.
Both are heavily discounted right now so you can get a great deal on either system. I think the RC-70s and Omni 15's are $399 (or $499) each and the centers cost around $299.
Mirage and Energy are sister companies that were Canadian based until Klispch purchased them. But they use different technology for these speakers. Energy uses the standard speaker monopole technology while Mirage uses Omnipolar technology which disperses the sound all over the room.
I haven't heard either speaker, but I hear mostly good things about both brands. Do you have any best buy magnolia stores that you could hear the mirage speakers? I hear that mirage speakers aren't for everyone, because of the omnipolar technology. Some people love the way that it sounds for surround sound movies.
I have a full 7.1 Mirage OMD set up with XT32 and I LOVE the way it sounds. Some people just have Mirage speakers for surrounds and have different fronts. They really shine as surround speakers and particularly when the speakers are directly to the left and right of the listening position. I never heard Energy speakers so I can't comment on those, I hear nothing but good things about them though.