These shelters are more similar to each other that different. The Twin Sisters would have an edge if you regularly face snow & winds thanks to the snow skirt but less good in conditions that you want ventilation.
I haven't seen the twin sisters in person, but I have see the earlier twin peaks, the beta light, and the shangri-la 2. All are well made. Of the three, I would be most inclined to the Shangri-La 2. Why? No deep reason… I was very happy with the GoLite Hex and more recently with the Shangri-La 4. Of course, I prefer the MLD SuperFly that was briefly made. Simular design made from spinaker which weights in at 11oz, 18oz with integrated bug netting around the perimeter.
My guess is that the differences in the reviews have little to do with the quality of the shelter, but the nature of the shelter. e.g., if someone disliked the Beta Light, they would dislike the Shangri-La 2.
There is a lot that is nice about these shelters. They can provide good protection in storms, a decent amount of room, with minimal weight. Ventilation can be OK when you pitch them off the ground. The downside is bug protection with ventilation. This needs to be handled separately or by installing bug netting around the perimeter after the fact.
If you are considering this sort of design, I would also consider a pyramid tarp. If you want an open, airy shelter then I would consider something else.
–mark