I've shot with a lot of cameras over the years. Notable favories are: Canon 5D Mark II and III, Sony a99, Fuji XT2, and the Nikon D750. I also used the D800 for a bit, but around that time I was still invested heavily in Canon. Eventually I bit the bullet and went all Nikon. First a D810, then a D750. I loved the D750, but missed some of the advanced features of the D810. So, biting the bullet once again, bought a D810. Luckily for me, I was able to get a great deal due to a promo Nikon was running at the time so I didn't take a loss.
So why this camera?
For me, one of the main reasons for choosing a camera is how it feels. Does it feel like an extension of you? The 5D Mark III was my all-time favorite camera. I loved that thing. It felt so good in the hand and the wheel on the back, oh! It was sublime. I miss it everyday. However, after getting used to the Nikon ergonomics I started liking the feel of the camera more and more. And once I read some set up recommendations from various photographers, I started tinkering with the more advanced features of customizing the camera to my style of shooting. The customization options on this thing are incredible, especially in terms of how it handles. I have spot metering on a front function button, next to my lens. I have back-button focusing using the AF-ON button on the back. I also have my record button to be quick access to my Auto-ISO settings. So whether I'm shooting the studio or on location, I know my camera is set up in a way that functions efficiently for the way I work.
The 36.3 MP Sensor in the D810 is beautiful. Images from 50 all the way to 6000 ISO look amazing. Sharp, detailed, and rich in color. Not to mention I have lots of cropping options for post-production. In comparison to say, the 5D Mark III, I find that I do prefer Canon's colors. However, my post-processing style has changed a bit over the years and now I have grown to appreciate Nikon's more neutral color palette. Speaking of cropping, the D810 also has the awesome 5:4 crop mode which allows me to shoot a more square like image right in the camera. I love that and much prefer this format to the traditional horizontal format in most cameras. It's a portrait shooter's dream. Does it rival medium format? No. But in the DSLR realm, the D810 is a frontrunner in terms of image quality.
Perhaps not a feauture of the camera itself, but in my opinion, it is Nikon, not Canon that has the best glass in the business. Especially when it comes to old glass. Modern optics are hit and miss for me, often favoring sharpening and corrections over character. Being a film buff, I love lenses with characters. The vintage Nikon catalog is full of all sorts of awesome lenses that offer superb image quality with this really nice 3-d pop reminiscent of what you'd expect from Zeiss glass. My current favorites are the Nikon 85 f/1.8AF-D and the Nikon 50mm f/1.4AF-D. I'll be adding more AF-D lenses to my kit. I love the look and quality from them.
Wrapping up, the Nikon D810 is a workhorse of a camera. I use it day in and day out from nudes to portraits and it can handle whatever I throw at it. I've shot about 30,000 images since buying it again in January and it shows no signs of slowly down. The build on it also gives me confidence as it doesn't feel as fragile as some other cameras. I recall loving the Sony a99, but within a month of using it, I had an issue with the shutter dial getting stuck. I've never had an issue with a single Nikon (or Canon) camera. As a professional, I need gear that's built to last. I think this is one of the many reasons many pros still invest in Canon and Nikon, there stuff works and it lasts.
I don't normally gush about gear, but thought I'd write a little tribute to my favorite little camera.