Looks like you have 3 great contenders there. Here are my thoughts on them:
1) If I recall the Prime Time awning was fairly far forward on the camper. When we looked at these (in 2011/2012), we couldn't figure out where a picnic table would go without blocking a door, or hatch, or anything else. Check it out on all 3 and imagine yourself at a campsite.
2) I like the Grand Design because you can get to the fridge with the slide in. You won't easily be able to do that with the other two.
3) Close the sliding bathroom door that goes to the wardrobe slide in the masterbed room in the PTM and GD. I felt like ones we looked at (neither of these brands) really closed well. Now, thing about taking a big stinky dump and being in the bedroom afterwards. Kinda gross, but something to think about.
4) The GD is the only one where the seats face the TV.
5) I love our U-shaped dinette and it was a requirement for my wife. Only the PTM and Sabre have them.
6) The Sabre shower is HUGE. I regularly have my 2 year old son in there with me and it's size is nice. Plus, I'm not small by myself.
7) Look at the layout of the outside kitchens and decide which you like the most.
Lots of good and bad, but the floorplan and layout makes or breaks it for me. We spent quite a bit of time in units, sitting and pretending to camp. I sat on the toilets to see when I had leg and move-around room. I climbed into the shower and washed my hair (the legendary long flowing mane that Timex loves so much).