My Nikon 'merry go-round' has actually been pretty straightforward. I use them exclusively for work, so my experience might be a bit different than many of you here.
I think my last film Nikon was an F100, then started with a Coolpix 5000, then went to a D70/D70s which got me a number of magazine covers as well as a couple of billboards (not bad for a 6.1mp camera!). Next I believe was a D200, then the D700 (kept the D200 as a backup), then currently the D4 and a couple of D800's for backup and video.
The D4 has likely well over 300,000 exposures. It died last year and I sent it to Nikon for a complete overhaul. It was a pretty quick turnaround and it now works like it always did. The D800's are fine, but for some reason I don't find that I reach for them as often as I do the D4. I'm using it primarily for architecture work (I do a lot of work for homebuilders, architects, interior designers etc), a fair bit of food for food manufacturers, plus some product and general commercial work. I'm not using it for any sports, though occasionally I've shot some sports for some of my school clients (I'm not great at it).
I'm going to be upgrading all my cameras next year. I've been going back and forth between getting the Z7 and the D850 -- I was leaning towards the Z7, but I just found out that the Z7 does not save an 'image overlay' in RAW (NEF), and that is a deal-killer for me. So the D850 it's going to be, though there is a possibility I'll get the Z7 as a backup. Either that or I'll have two D850's.
The only other digital cameras I have are my Leica M's -- maybe I have dumb luck or something, but I really haven't had any of the trials and tribulations that others here have had. My M9 was great, though the stupid 8-frame buffer drove me nuts. The first Monochrom suffered from the same malady, but other than that it was a good camera. The M246 has been great, as has the M-D 262. Hate to say it, but I'll likely buy the M10 Monochrom with the 41mp sensor when it comes out next year -- my Leica 'pusher' already has me down for one when they're available. I'll probably hang onto the M-D, as it's such a unique and wonderful camera.
I'm almost embarrassed to say that I'm down to one film camera (a Ricoh 500 with the bottom trigger wind) that someone gave me last year. It's a real beauty, but it has the same roll of film that I put in it last year. Guess I'm not much of a film shooter any more