Despite my iPhone passing into unconsiousness as I type this, the Apple store in the city has always been extremely helpful. Entering the store feels not dissimilar to being part of an 80s game show with people there to greet you with extreme Apple enthusiasm. the decor and music are supremely Steve Jobs, and I really don;t think there's anything the staff can't do. The product range is space aged and aesthetically beautiful. If they don;t have the phone for you, then it probably doesn't exist yet.
I like the Apple shop in Perth -I find the buzz exciting in there though I have to admit, sometimes you can wait just a bit too long despite being greeted at the door and directed to somewhere.
I find all the staff are friendly and willing to help.
As for non-Apple brands, I used to just buy anywhere and always buy outright