Bre'r Dan,
Wheelhouse!
I've cooked on a Backwoods a Party, a couple of Fatboys, and a Competitor. Also, once on an original Stumps (whatever they call that model now).
While I preferred the Backwoods, it was largely because the Stumps jammed -- a problem which has been solved. They're both really well made, insulated cabinets which function pretty much the same -- You probably can't go wrong with either.
Rust sounds more like a care issue than a design defect, but I'd look into it on the Backwoods forum before purchasing. For that matter, both manufacturers maintain enthusiastic forums. The collective knowledge bases are fairly large and there are plenty of honest owners -- you should definitely visit.
Another type of insulated cabinet worth thinking about is a Cookshack. If you've got electricity on your patio you might want to take a serious look at the AmeriQue as well as the model just under that. Another possibility -- but probably out of your price and size range is the Fast Eddy (also a Cookshack). You can compete KCBS with them -- but not the more "electric" Cookshacks. There's a similar series of cabinets to Cookshacks with "Texas" in the name, but I forget the exact name offhand.
The issue with all cabinets is air flow. You can't load them up in such a way that the heat and smoke can't circulate. You can buy a Backwoods with a convection option (costly, though), but they're really only
If I were ordering a new smoker tonight it would either be a Backwoods Fatty, Comp or (in my dreams) Piglet.
Horizons are indeed well built -- if a little crudely designed. However the basic mods only take a few hours -- including the drive to the hardware store, parking, etc. So don't let that deter you. If you want an offset -- on the small side of medium, just barely large enough to be a true "stick burner" with a lot of trouble -- it's a decent choice. If you look around you can probably find steeply discounted Brinkmann Longhorn cookers as well. FWIW, the basic design is called "Longhorn" by pretty much everyone BUT Horizon.
While Longhorns can serve double duty as grills in a pinch -- iin my opinion it's not a great choice for someone who does a lot of grilling. There's no way to adjust the difference between the charcoal and food grates and you don't exactly have the same air control as with a Weber. At least not in the cooking chamber. FWIW, the big offsets put a grill on top of the firebox, which does have plenty of air control.
There are much better pipe section and square section offsets. Klose for instance which come fully "tuned." (
Got there before Mary! 
) Another great choice would be Lang which use a "reverse flow" design to take care of the tuning. Let me plug another really great manufacturer -- and that's Peoria.
barbecue pit smoker trailer custom barbecue pit Peoria Custom Cookers
They can and will build you an excellent combination smoker/grill with a "Santa Maria" style high-rise food grate to boot. But it's a custom and will set you back a few bucks. They're also on my short list.
If you're interested in ultra convenience you might also want to consider one of the pellet burners like Mary's new Traeger. They're really very good.
Your most bang for the buck -- portable, good grill, excellent smoker is a Weber Smokey Mountain (
Why kokopuffs! Is that you? 
). The new 22-1/2" WSM looks like it's got plenty of room. You can pack the 19" pretty well and feed an army, but it's a little too small if ribs are your thing. That said, the 19" is the ultimate portable.
Finally, you're in the right price neighborhood for some of the lower priced ceramics like the Big Green Egg and the Primo. You're not going to get the same capacity as a Party or even a 22-1/2" WSM for that matter -- but it does most poeple pretty well. Excellent smokers, excellent grills. The range of temperatures they can hold steadily for long periods with very little fuel is eery.
Since you're looking at Stumps and Backwoods you're undoubtedly aware of the BBQ Guru. I know they're expensive, but if you get anything other than a Cookshack or Trager type -- go Guru, and go wireless. They free your life up considrably and since smoking is usually a weekend thing -- that's important!
Let us know how your thinking develops,
BDL
smoker question; looking at backwoods party or a baby stump 
which led me to look into the Baby Stump smoker. It's a bit different type of vertical from the water Backwoods...but still seems to be a good smoker just the same (some say better).
(and on that note...thanks for your post BDL, it's always appreciated.
