UKC

I'm considering getting a used Canon R6 - body only.

If you could only have one lens for it - what would you get? Initially I'm mostly interested in climbing photography, mostly portraits - either closeups or wide shots so wouldn't need to be telephoto.

For my EM5 (M4/3) I have a 12-40mm f2.8 PRO lens which I really like - so maybe something similar?

Interested to hear others' experiences.

My most used lens is the RF24-105L, it’s superb. Unfortunately I’ve managed to scratch the front element. I’m also thinking of selling it (and all my Canon mirrorless kit) if you’re interested. I’ve done several tests to see if I can pick up artefacts from the scratches and can’t find any effects at all but obviously it’s going to dent the price somewhat.

Let me know if you’re interested.

I'll most likely go for a supplier that provides a warranty but I'll bear it in mind - thanks.

When I had a Canon my most used lens, by a long way, was the 24-105. It wasn't my favourite lens, but it was the one that was most useful for almost every situation. 

I normally carry at least 2 lenses with my R6 (all older EF lenses, used with ef-rf adapter) but if I could only have 1 then yes, ef 24-70 f2.8 (cheaper) or rf 24-105 f2.8 (expensive)

As the poster above said, you'll need the adaptor for EF lenses. You may get a weird ring appear in the viewfinder if using EF lenses on it but don't be alarmed, you can sort it out in the menus. 

The adaptor will make the whole setup much bigger, naturally. 

For climbing shots you'll want something quite wide and for the portraits, medium long. I agree with the 24-70mm ish suggestion above. I use the Sigma Art lenses and they are amazing for the price and quite fast. I'd definitely try to get a fast lens from the outset, if you can afford to do so. 

I use an EF 24-105 F4 L IS with an adapter ring and an RF 24-105 F4 L.  Mostly I use the later as it’s a staggering lens and when I can use my feet it does almost everything I want; most of the time when I want a wider shot it’s a daylight landscape and my iPhone does well enough.

I greatly enjoy using a couple of a third party prime lenses with manual focus; the Rokinon 85 mm F1.4 and the Sirui 55mm T1.2. You can set the focal length manually for the IBIS and the EVF zoom and focus peaking makes focusing them a breeze.   You can do action shots with them with practice and a bit of anticipation.  I’d like full autofocus prime lenses with the same max aperture but even man maths balks at the price as a non-paid photographer.

Something changed with the new short back focal length mirrorless mounts like RF, and these third party lenses get fantastic quality compared to those from the EF era.