I've been a Canon user for a very long time - I bought an EOS 650, the very first EOS camera (i.e. not the 650D), in 1988 when it was still the current camera. Since then I've had several film EOS cameras, plus several EOS DSLRs, starting with the D60 (yep, a Canon D60). Currently I'm using a 6D and 750D (T6i).
I'm not someone who is able to pick up a strange camera and be efficient with it quickly. However, there have been enough similarities between all these Canon cameras for me to be instantly comfortable with all them as I got them. I did make a brief excursion into Nikon-land with a D70, but although I appreciated the quality of the images I got, I never, ever got used to the differences between the Nikon and the Canons. The way the main control dial was horizontal (on the front of the handgrip) instead of vertical (on the top of the handgrip); the way the focus ring ran the other way; and several others. I also tried a s/hand Olympus OMD-M10, very briefly, but I couldn't get on with that at all!
So you could say that I'm a Canon user because I can't be bothered to learn other systems, and there's some truth in that. But does it matter? I have been tempted by Nikon in recent years, especially since the Sony sensors' better DR was revealed. But there aren't that many times when it's a deciding factor so I'm sticking with what I'm used to. In the last couple of years I've also started getting some prints professionally printed, at significant size (20" x 30") and frankly I'm knocked out by the good ones; and the less good ones are "less good" as a result of a failure in the photographer's vision, not the technical aspects of the equipment.
So I'm sticking with Canon because it's what I know. That's not all negative - I honestly think that after 30 years, nearly, of using Canon (D)SLRs I'm so accustomed to them that the strangeness of different, better equipment would itself come between me and achieving the better results the alternative system could (allegedly) produce.
Finally, there is the question - are the alternatives actually better? The Sony sensor certainly produces greater DR at base ISO, but I'm not sure of the extent that's visible in practice. I don't mean at 100% on screen - I mean in a 1000 x 1500 JPEG on-screen, or a print - the former will have surrendered detail, the latter will not be able to display the full range that might have been captured because the medium - paper - simply doesn't. Then there's DPAF, which I don't believe any other manufacturer has.
So there's absolutely no need to think that Canon is a second-best choice. It has its strengths and weaknesses, but so do all systems.