I am a rare bird around here.
For my birds in flight, and fast action sports photography I use two Nikon D7100s. These cameras with fast Nikkor telephotos are simply outstanding.
For my serious landscape/nature photography, I was an early adopter of the Pentax K3ii APS-C camera. It was the first Pentax camera to come out with high resolution/pixel shift mode. It must be used on a tripod, and can only be used if the subject does not move (even a gentle wind will result in ugly artifacts). However, the K3ii 24mp camera (when used to shoot a motionless subject in the pixel shift mode) will produce images that rival the results obtained by a Nikon D810.
The new Pentax K1 full frame camera has an new updated version of pixel shift that is claimed to allow one to photograph objects that move! This is truly revolutionary "if it works". In the next month or two we'll all see comparisons of the Pentax K1 pixel shifted images to the D810 and even to medium format digital cameras. If the new K1 version of high res pixel shift works as advertised, the K1 may just be the best landscape/macro/nature DSLR ever made.
Actually, I have nothing to complain about when it comes to lenses that I can use on the K1 full frame. Pentax currently has about
80 lenses (
http://www.pentaxforums.com/lenssearch/?inproduction=0&format=ff&focusing%5B%5D=af ) that you can purchase new that are high quality and cover a full frame sensor. Also, there are literally millions of old MF and autofocus older Pentax K mount lenses out there that will also fit and operate nicely on the new Pentax K1 full frame camera. As for me, I'm a fan of manual focus, and already have purchased 5 Zeiss ZK lenses and 3 Voigtlander (Cosina) lenses that I intend to use on my K1 when it arrives in April or May.