I commute from Denver to ORD. I was in LGA because of the short reserve time as a NH, but am holding a great line in ORD now after about a year. The commute from Denver isn't bad, and I routinely pick up trips in DFW. If you're going to commute anyway, and have no ties to DFW, I would suggest ORD. There are a ton of flights on United, and American has options also. There are more flights on American to DFW, but like Pedro said, they are almost always full. Denver is a popular destination for Texans, and you'll end up in the jumpseat a lot. In a year going to LGA and ORD, I haven't needed to use a commuter clause once.

If you have any other questions, feel free to PM me.