One quick thing to look for is a arched/crown roof (Jayco calls it their Magnum Truss). It is almost and industry standard, but any company NOT using it is trying to save a buck.
"Rubber" roofs are pretty standard, but take a lot of maintenance (inspections, washing, UV protectant, caulking) if you want it to last a long time (or park it under a roof). Fiberglass or aluminum are better, but not common ($$$).
There is, what seems to be, a never ending debate between wood/fiberglass insulation/aluminum siding and aluminum/solid foam/fiberglass siding. Both have their positives and negatives.
Some of the "light weight" models use aluminum frame/foam core/composite floors (very similar to wall construction). If not properly engineered, these will get soft in high traffic areas. Many companies gave up and went back to plywood.
Pocket screwed cabinet frames are much stronger than stapled.
If you are serious about a 5er, try to find one with a residential refrigerator, unless you are planning on doing a lot of boondocking. If you do decide to go with a residential refrigerator, the battery box should hold two 6V golf cart batteries and the unit should include at least a 1000W inverter. Converter/chargers are another place where companies go cheap. You are better off with a top of the line inverter/charger with built in transfer switch and just a "dumb" DC distribution panel.