Upload & Sell: Off
The Henry's locations I've been to (in the GTA) unabashedly hard sell you on everything on every visit. I've walked in asking to check out a specific lens/camera, and when they didn't have the desired item have persisted in asking if I'd like to try out something complete different, even after clearly explaining that I am only interested in a specific model. A visit never ends without a "shall I cash you out," even if I have come in with my body/memory card, and clearly explained that I'd like to take some test shots for review (at home in lightroom). Many of their salespeople are relatively unfamiliar with the finer (or even more significant) differences between products, yet will still try to guide you in a certain direction "as an expert." There is always a heavy "are you going to buy it or not" attitude. By the shear number of Henry's locations compared to other shops, it is clear that their business model is shifting towards mass retail. Some locations might be better than others, but I've never happened across one I've liked.
By contrast, I've found the Vistek locations I've visited (Downtown Toronto & Mississauga; the latter being my favourite even though I live downtown) to cater much more to the enthusiast. If I ask to try out a specific lens and they don't have it, they just say, "Sorry, we don't have one at the moment." If you come in with a body/memory card to try something out, they understand that you are not interested in purchasing it then and there, and give you their business card. Their staff (for the most part) are enthusiasts themselves and understand the finer points and won't try to sell you on something you're not looking for. I've even had staff suggest things like, "It sounds like you really ought to try to buy a used D700." They'll also deduct the rental fee from a new lens if you want to rent it for a weekend to try it out. I've heard Vistek can be sort of intimidating for people new to photography, but I see that as motivation to learn more before buying new gear.
Aden seems to compete solely on price. They are usually bottom dollar, but don't seem to keen to have people trying out lenses and whatnot. I've also heard they're pretty hard on any sort of returns/warranty stuff, though I don't think I have ever had to return a lens anywhere. Downtown Camera is a nice medium. It often has significantly better prices than Henry's or Vistek, and the staff I have dealt with are nice, helpful and not at all pushy. I haven't had any experience with online retailers; I like being able to physically go somewhere if there's a problem.
If the price difference is relatively small (say $50 or less on a $750 and up lens/body), I'll usually give Vistek my business. I've gotten some great deals from Downtown Camera, and would do it again. I'd buy from Aden if they had a killer price on something that I knew I wanted and wasn't going to have issues with. I'd only buy from Henry's if there were serious price/availability benefits over Downtown or Aden, which is highly unlikely.
Just my two cents; I'm sure others have had different experiences with the different stores.