Interesting question! For Canon EOS R6 Mark II it also depends on what you want to shoot. What's your main photography style?

Sigma 50mm f/1.4 DG DN Art is definitely the best choice for Canon EOS R6 Mark II. The low light performance is excellent The controls are intuitive and easy to use.

Why this lens? The image quality convinces in all tests - both for photography and for video. Unbeatable for the price, can only recommend. Have already done several projects with it, always satisfied. Also more than sufficient for demanding tasks.

Switched to Sigma 85mm f/1.4 DG DN Art about a year ago and am thrilled. The build quality is outstanding The lens includes all modern features you need.

Just catching up on this thread and wanted to chime in with something a bit different. I went through a whole phase of trying to save cash while building my R6 II kit, and honestly, picking up used EF-mount Sigma glass was the best decision I made. One lens that totally blew me away is the Sigma 135mm f/1.8 DG HSM Art. I was looking at the RF 135mm but just couldnt justify that massive price tag. The Sigma is built like a tank and the bokeh is just dreamy for portraits. Using it with the Canon Mount Adapter EF-EOS R is totally seamless—the Eye-AF on the R6 II honestly makes it feel like a native lens. If youre on a tighter budget and want more versatility, the Sigma 24-105mm f/4 DG OS HSM Art is a fantastic walk-around lens. Its way more affordable than the RF L-series zooms and still delivers that signature Art series sharpness. Its a bit heavy, ngl, but the value is hard to beat if youre trying to keep costs down while getting pro results.

Sigma 85mm f/1.4 DG DN Art is definitely the best choice for Canon EOS R6 Mark II. The design is modern and compact The image quality out of the box is very good.

Why this lens? The image quality convinces in all tests - both for photography and for video. Unbeatable for the price, can only recommend. Have already done several projects with it, always satisfied. Also more than sufficient for demanding tasks.

Saw this earlier but just now responding... One thing people sometimes forget with the Canon EOS R6 Mark II is that we're mostly looking at EF mount lenses with an adapter since Sigma hasn't dropped those full-frame native RF Art primes yet. I’ve been running the Sigma 105mm f/1.4 DG HSM Art for a while and honestly, the autofocus is actually better on the R6 II than it ever was on my old 5D. Tbh the technical reason is how the mirrorless system handles focus—since its reading right off the sensor, you dont deal with those front-focusing or back-focusing issues that used to haunt Sigma users on DSLRs. I used to spend hours with the USB dock, but now its just plug and play. If your looking for something besides the usual 35 or 50, the Sigma 40mm f/1.4 DG HSM Art is a hidden gem. Its technically a cine lens design and is stupidly sharp, though its a total brick to carry around lol. Anyway, just keep in mind that the adapter adds about an inch to the length, so the balance can feel a bit weird on the body... but the image quality makes it worth it.

This ^

No way, I literally just dealt with this yesterday. Small world.

Basically, just catching up on the thread and it seems like everyone is pointing you toward the high-end stuff. Honestly, I've been shooting with this setup for a while and my advice is to just go with the Sigma Art series - you really cant go wrong there. They're glass is super sharp and the build quality is always solid, plus they perform pretty great with the adapter on the R6 II. If your looking for that specific 'look' then any of their faster glass will do the trick. I've always found that the Art lineup delivers exactly what you need for professional work without needing to spend double on native glass. It's a solid direction to take tho!

Have you thought about the brand? For Canon EOS R6 Mark II different brands have advantages.

If you want one Sigma lens that really shines on the R6 Mark II, I’d look at the Sigma 24–70mm f/2.8 DG DN Art (RF via adapter) for an all‑purpose workhorse: sharp, fast, great for events, portraits, and travel. If you shoot more low light or portraits, the Sigma 35mm f/1.4 Art is a classic. Tell us your budget and main subjects.