This is what National Geographic had to say about the two cameras:
The OM-D E-M1MKII is the best wildlife camera in the bunch. The combination of dials, buttons, and lever toggles lets you change settings faster than on most other imaging systems, compact or professional grade. The weather sealing rivals that of top-tier professional DSLRs with a fantastic grip for its size. And the lenses! All the pro line lenses have a high-build quality that can take whatever you throw at them and sport wonderful features, such as integrated lens hoods, smooth zoom/focus rings, and round bokeh, or background blur. As a micro four thirds (MFT) camera, its sensor is small, giving you long reach from physically smaller lenses, such as the 300mm (600mm equivalent). The ability to carry a small backpack with a few small lenses, fantastic ergonomics, excellent image stabilization, all-weather durability, and high-speed performance means a potent wildlife photography kit that won’t weigh you down when you’re on the go.
The DC-G9 is comparable to the Olympus OM-D E-M1MKII but comes out ahead in video. This camera has a full-size HDMI, better ergonomics for waist- and chest-level video shooting, and more options for capture rates and color profiles, plus a convenient electronic viewfinder and roomy eyecup. And unlike the more classical AF system found in the OM-D E-M1MKII, the DC-G9 uses Panasonic’s DFD (Depth from Defocus) technology, which provides better results in photos of people, still subjects, and animals with a firmware update, though there can be issues in high-speed situations. Another perk for videos and stills? The IBIS system, which integrates well with Panasonic’s stabilized lenses. The DC-G9 is larger than other cameras on this list, but a pro-style top-down info screen makes up for its size.
Tip: Pair the DC-G9 with the wonderful 12-60mm (24-120mm equivalent) kit lens, and you’re good to go for most subjects on your travels.