We used an original Rainshadow when our daughter was younger. It easily sleeps three people with most of their gear inside (except packs.) It's a very good tent, and I expect the new version will provide more headroom for hanging out. When my wife and I used it on 2-person hikes, it worked pretty well.
After a while, though, I got tired of the single front entrance/vestibule, and pushing my gear out of the way to get out of the tent. I wanted two doors, two vestibules, and the doors on the long side of the tent. We used a Tarptent Double Rainbow for a year or so, but found the interior volume cramped due to the design. (Otherwise it's an awesome tent.)
The Lunar Duo is amazing, the largest interior of any lightweight 2-person tent we have tried. The two vestibules are large enough to hold all our gear, and the long side walls/doors are vertical, so we can leave the canopy doors open during light rain for ventilation. The interior is long enough for a tall person in a long sleeping bag, and neither end touches the mesh wall. The canopy doors are adjustable at any height, so I can have ventilation even in wind-blown rain. The main canopy over the sleeping area is a single piece of silnylon, so there are no seams to leak. It holds up very well to major rain and wind in our experience.
The LD is a little tricky to set up, and I still find myself fussing with it even after a couple of years of use. (The Double Rainbow just pops up completely taut. The Rainshadow requires a little fussing.)
As for your choice, it's not really a tie -- if you will need a 3-person shelter at some point, the Rainshadow is the only option. But if you are comparing these as 2-person shelters, the LD is an excellent choice. The overall design, with 2 doors on the long sides, is much more usable in my experience, and the interior volume provides enough space to have 4 people share a meal (or the proverbial game of cards...)
Have fun in the canyon.