With a $50K limit you can look at 5ers with MSRP of around $70K and negotiate the rig's price down. As for which brand is better of the ones you mentioned, it really doesn't matter as they are all slapped together as fast as they can push them out the door.
Get the floorplan that works best for your situation from a dealer that prides itself on great customer service since no RV manufacturer builds a defect free rig you are sure to require warranty service. Been to ever so many RV shows over the years and have seen flaws from every manufacturer on every rig I've walked through, no biggie as a quality driven dealer will easily remedy most issues. Happy shopping!!!