All depends on where you are going to be living/staying. And your going to get a different opinion from everyone. I'll try to give u an unbiased opinion, well as much as I can from when i lived there.
Aqua sport: Charlene and here crew are good people, she has great prices and is very easy to deal with. Every time I go there it is a pleasant experience.
Leisure Dive: relatively a new shop in town, well it is out in Airdrie. This by far is the best service store I have been to, guys is a machine at servicing regs etc. Darrin also use to be the owner of the dive Shop which he has sold to their current owners awhile back. Anyways he has great prices as well and works with aqua sport as well.
Adventures in scuba: just up on mcleod trail about 4-500 m north of southern if i remember correctly. Well this shop tends to run with a quite bit higher prices then the rest. Friendly staff and they have great attitude, etc.
Dive shop: located by the hooters on mcleod and the heavy metal bar(drawing a blank on the name, back alley i think). This use to be owned by Darrin that now owns leisure dive out in airdrie, I have yet to shop there under the current owners. My thoughts are that it is probably run pretty much the same, slight variances etc but that shop was the largest in town and probably still is. I'll have to check it out though next time i am in town.
Caribbean dreams: basically follow glenmore trail west to the casino and it is right around there. I was only in this shop once it is relatively small and is more geared to warm water diving. I do believe though that they have gear for the area as well.
Considering i no longer live in Calgary take this all with a grain of salt.
My opinion, go to aqua sport or leisure dive they are great spots to go for rec/tech diving,they will not steer you wrong and are great people. I am sure the other will give you good service but those are my two choices of shops when I am back in town.
Regards
Steve