Heartland builds entry to mid level trailers. The difference between a Big Horn and Landmark is the Landmark is a loaded up Big Horn. In other words more standard options. That is what I found when I was looking. I bought a Redwood which is a notch above the Landmark. The Redwood construction is more solid because it used marine grade plywood rather than particle board and has 16 inch centers on the rafters rather than 24 inches and 3/8 ply on the roof rather than 1/8 lauan. The Redwood suspension is more robust than the Lippert. The Redwood costs slightly more than the Landmark, but the small price difference is worth it.
The Heartland forum is nice and the owners are nice, but the same can be said for all of the other owner groups. After all they all want to support their purchase decision and do everything they can to keep the resale price.
Both Redwood and Heartland are owned by Thor so there service and warranty will be very similar.