Back in the 2006-2007 era I bought a Canon 20D and then a Canon 5D. I had a Sigma 18 to 125 mm for the 20D and a 50 mm / 1.8. I also had the Canon 580ex II Flash. With the 5D I bought it with the 24 to 105 f/4 L IS-USM, and then added the 50 mm / 1.4, the 85 mm F 1.8, the 100 m m f / 2.8 macro, and a 70-200 f / 2.8 L IS- USM. In other words I had about a $10,000 system which I shot for about five years alongside my much larger and more extensive Nikon system. At the time I was shooting the Nikon d2x, which was in some ways a remarkable camera, and in other ways was not that great. The 5D's image quality was extremely good, but it was based upon a roughly 25 year old EOS 7D film body. It was in other words a $389 camera with nice new digital innards, but it was in most ways not that great a machine. The D2x on the other hand was a $5,000 camera in the spring of 2005, and it was roughly the 4th or 5th Pro Nikon made since 1995 . In 2012 I got a great deal on a used Nikon D3x and that pretty much spelled the end of the use of the 5D. The D3x had almost twice the megapixel count and was a vastly better machine than the 5D in every single way, and I mean in every single way-- battery life, focusing, viewfinder clarity and brightness, customizability, voice annotation, file quality, buffer depth, frames per second, build quality, exposure accuracy, quality of viewfinder display, and so on. I gave Canon a good chance, but I never really did like it as much as Nikon. At the time the D3x was the best sensor with the widest dynamic range and the greatest amount of exposure recovery possible in 2012. It was a great camera and it had a fantastic sensor, and it worked as I wanted it to work with both autofocus and with manual focus lenses. It had a spectacular flash accuracy with the sb28, and so I was happy to leave Canon behind for good.
Around 2015 I decided to sell off almost all of my Canon gear...i kept the 20D body and the 5D body, and kept just the sigma 18 to 125 for the 20D. I sold off all my Canon lenses . Canon EF cameras work quite well with adapted lenses from seven legacy 35mm systems, and I have about 10 Nikon to Canon EF adapters, and I have a couple for Pentax thread mount, and one adapter for the single Olympus OM lens that I have. I really never did like the way the Canon cameras' controls were configured. A number of very important things are backwards from Nikon. Lenses mount in the reverse direction, focusing is in the reverse direction, the f/stops change in the reverse direction, the Canon control dials change function based upon which exposure mode the cameras is in! After about 20 years in the Nikon system I never felt completely at home with any Canon. The last time I took my Canon 5D out to shoot was do a steampunk Disney shoot, and after three frames, the mirror fell off of the mirror frame, which was a well-known flaw in the 5D design and manufacture. Around 2010 or so Canon offered a free fix of this problem on a recall, but I did not send the camera in, which was unfortunate . There were no clips that held the reflex mirror on to the frame, just glue! As I said the original 5D was an inexpensive body and it was not built to be as tough as let's say the Nikon D2x or the Nikon D3x.
I can understand how a certain camera brand can feel right to a certain person and two other people might each have their own favorite.