As far as which model, it is very dependant upon each person/couple, they are both good trailers.
For us, we prefer the bed as far away from the door as possible mostly because I am a much earlier riser than my wife and this gives here more privacy while I putz about and go in and out. I had skipped the 21 when it came out but did end up going with the 5.0TA.
The 21 is 4" wider which does make the walkway easier for two, though we never had too much trouble ourselves in the 19 as there is little reason for two to go there at the same time, whereas with the 21 you have to get to the dinette.
The location of the dinette matters to some, with some liking the rear dinette. We have this in our 5.0TA and there are a few times it has been a nicer view when sitting at it. The thing with the 19 is, that it is almost always open in front of the dinette, and we find that in most campgrounds we back into trees, but the few where you are open to water or a view are nice. With the 19 we loved the dinette near the door for use as a marshalling area and should my wife be cooking inside to enter it does not affect her at all. All this said, we only use our dinette inside when it is real ugly outside, as we prefer to cook and eat in the great outdoors we came to see anyway.
The layout of the 21 gives a larger feeling when entering with the most open space being by the door which is nice.
The bathroom in the 21 is a bit larger, but for us we are fine with the 19/5.0TA bath size as it is plenty big enough and allows for more storage of gear. If camped at a place with washroom facilities I mostly enjoy the stroll there to use them, getting the chance to meet others on my walk, and Jasper loves any excuse for a stroll or running beside the bike.
The bed in the 19 is a full queen with the only negative being installed E-W which never really bothered us but some do not like. The bed in the 21 is easier for two to get into but is narrower than a queen by a few inches which might matter to some (like my wife
In the past there have been many comments on wishing there was a 21 with a 19 layout, to give the bigger size with the layout some prefer.
I would highly recommend you check out both closely. Heck, even do a weekend trip to the area of the Escape shop and see them both together there, lots of great places to check out while you are there. We have flown in to Abbotsford a couple times to have a meeting at Escape and to spend some time in Vancouver which was great fun.