Faststang, if you get a vertical cabinet smoker [square with front door(s)], they hate being off-level, and the legs need to be spread-out snugly when you set it up. This will give the best fit and seal on the cabinet door. I have to remember to do this with all of my cabinet smokers if I move them. Also, some tweeking can be done if there are mild to moderate leaks around the door which will re-align the cabinet/door for a better seal if it still leaks after being leveled properly...been there, done that
None of the less expensive smokers will be prefect, and few high-end smokers will, either...so, you live with the imperfections, or do a little bit of work to iron out the wrinkles, and then you're good to go. The heavier the metal that's used in construction of the smoker, the better, in most cases...you will pay extra coin for the heavier units.
Let us know if you need help identifying the causes of any more issues, or need help deciding which one to try next. Sometimes we are limited to our local sources, and stock may not be what we'd like to see, so choosing which is the better of a small selection may not be your favorite decision to make.
You may want to look over the forums on charcoal smokers, propane, and vertical vs horizontal to decide which type may be to your best advantage. If you start with a smaller cabinet smoker, you are limited on what you fit into them, so if brisket or full slabs of ribs may be on your menu in the future, keep that in mind. Wide-body vertical smokers may be more to your liking, but if you don't mind a little more fire tending and would like the ability to char-grill on the pit, then a charcoal-fired horizontal of a decent size will handle most anything you can throw into it, within reason, although there are a few horizontals which are not well-designed for use as a grill, but work reasonably well as a smoker. Lots of mods can be done for horizontals (tuning plates, baffle plates, lowering the exhaust vent inlet, charcoal baskets, etc), so look for them in the charcoal smoker forums as well.
Eric