SYSTEM weight (defined as the weight of the camera bag you carry around) will not change significantly if you keep using full frame lenses. For most of us, lenses are where the weight is. Oh, you can settle for smaller maximum apertures and save a bit of weight, but if you like to work in low light, that's annoying.

I have used many cameras, both personally and professionally. Today's cameras are incredible — period. I would rent to try before you buy. Basically, menus, ergonomics, weight, and feature sets matter a hell of a lot more than brand. All of the majors are making great bodies and lenses now. And since most of the mirrorless lens designs are less than ten years old, they benefit from the current state of the art.

That said, life is full of little trade-offs. EVERY camera is some sort of compromise. You give up some attributes to get those which are mutually exclusive. We can't buck the laws of physics.

My personal system is Micro 4/3. I use a Lumix GH4 for both video and stills. I have three pro-grade stabilized lenses — 12-35mm f/2.8, 30mm f/2.8 Macro, and 35-100mm f/2.8 (equivalent to full frame 24-70, 60, and 70-200 mm range), plus a couple of f/1.7 primes (15mm and 42.5mm). My entire system will fit under an airline seat. My bag is half the weight of what it was in my APS-C dSLR days, and 1/3 the weight of my kit in the film days of my youth.

I can, and have, written 7-page explanations of why I use what I use. It DOES NOT work for everyone, but it is exactly what I need. The best advice I can give you is go to http://www.dpreview.com and read reviews of the latest gear in your budget range. Then rent, and give the rental gear a good workout.

I would carefully define what it is you want to photograph. Define a kit weight you can tolerate. Define what is most important to you about a system. Define a budget. Then look for gear that meets your needs as best as you can find. Every body and lens has its niche application.

If it's Micro 4/3 you want, the Lumix G9 and GH5 are top-tier machines. Both are particularly good at BOTH stills and video. The G9 is the better stills camera, and the GH5 is the better video camera.

The Olympus OM-D E-M1 Mark II and the OM-D E-M1X are also top-tier. Others here have sung their praises.

If you like APS-C, the Fujifilm XT-4 is my target pick because their lenses are specifically designed for THAT FORMAT. Its film simulations in JPEG mode are great.

I'm not going to get into Sony, Canon, and Nikon offerings. Others will tell you their stories. Suffice it to say their mirrorless offerings were not there when I was in need of a new system. If a full frame mirrorless system were available in 2014, I would have bought it, so long as the audio features of the video section had pro features.