Jason, we prefer the Long over the Twin for two people. It gives more space for two overall, though as I said, there is a little bit less room in the center at the back, because of the vertical back wall on the Twin. For us, the extra space at the head and foot on the Long compensate for this as that is where my wife, who sleeps at the back, is more likely to brush the fly on the Twin. However, your build and sleeping style may make a difference; we're both a fairly slim build and sleep close together. Neither the Twin nor the Long have a lot of width for a couple who like to leave a lot of space between them. You have to be prepared to sleep with touching mats. In return, you get a 2-person shelter that can set up in some pretty tight spots (and weighs very little).
It should be noted that although the Twin and Long have the same footprint, the geometery is quite different, not just because of the Twin's back pole vs the Long's two sidepoles, but also because of the Long's higher main pole height, which gives more room to sit up over the Twin.