I never usually get into these threads about "which is better" but you asked for input from owners of specific make/model trailers so I will comment.
This is our 6th RV over 35 plus years and we couldn't be happier. It is our nicest to date considering the price point. We wouldn't trade it for anything.
We traded a 2011 Cougar against it and, although we took a bit of a hit trading such a new unit, it was well worth it to us. We felt the Cougar was more of a weekend camper trailer and this is much more refined and capable of long stays. The construction quality is vastly superior (IN OUR OPINION).
We have had it now for just 1 year and have traveled almost 20,000 miles and lived in it for over 4 months of time with the longest rip being 3 1/2 months all around the US.
We never intended to go to 33 ft long (our Cougar) let alone 36 ft, which this is, but we wouldn't trade it for anything. We love all the storage and the rectangular shower is a huge plus. We love the interior appointments and we got the 12 cu ft double refrigerator that we love. We also added an A/C to the B/R that proved invaluable on our cross country trip. I put an Onan in the front compartment but that was just for my convenience.
Oh, it is far better insulated than our Cougar was and very easy to heat and cool. I also love that the B/R slide is deeper so there is much more walking room in the B/R.
Were there some issues to be resolved, yes. I've never bought new or old where there weren't a few things to be addressed but nothing you would even remotely consider major and one of the most incredible pluses about this trailer is the company. Incredible customer service. I have the email addresses and even phone numbers of all the main players in the company. They walk the talk.
I'm sure others will chime in but if you have any specific questions about the Reflection 337RLS, feel free to ask me.
Paul "Poppy" Cervone
2016 GMC Summit White Denali 3500HD SRW CC/SB
2015 Grand Design Reflection 337 RLS