I agree you with Chrysler's quality, or lack of. I have seen some pretty bad Chrysler vehicles lately. Chrysler or Dodge doesn't have any vehicles that appeal to me at the moment. The Magnum isn't a bad design, it's actually somewhat decent. The dodge trucks have the Cummins, which I think is the best diesel out there in pickups - Cummins > Powerstroke > Duramax.
Mercury doesn't seem to be upscale more, but it seems to be more marketed to members of the female species ... don't know why, but it just seems that way. Would it keep me from driving a Mercury - no. If I could get the same exact vehicle with a Mercury badge for less than the Ford equivalent, I would go with the Mercury.
GM isn't my favorite, but they do have a few vehicles that I do like. Buick LuCerne and LaCrosse, Impala SS, Tahoe and Suburban ... their trucks since around 00 never impressed me, the quality went down.
I can't really rant on Ford ... yes Ford does build bland vehicles, but I like bland vehicles somewhat. I am not happy that the Expedition has a 4 wheel independent suspension (at least the Tahoe and Suburban have a solid axle - a MUST in any sort of truck/SUV application), and the same goes for the Explorer and Sport Trac. The Ranger is due for an update, but it is a cheap and proven design. A ranger with the 3.0 Vulcan V6 will run for a couple hundred thousand miles provided it doesn't have an early death (wreck, rust)