I have a wireless IP camera on the side of my house that always struggles to connect as it's quite a long way from my Vigor 2860.

What's the best range extender to use with the router. I guess Draytek make some which are probably best to use with their own routers.

Depends what you mean by "range extender" - do you mean an access point which can be wired back to the router, an access point which will connect to the router via wds bridge mode or an access point set up in "extender" mode ?

And no, Draytek APs are not necessarily your best option.

I can't wire it back to the router so I guess an access point which will connect to the router via wds bridge mode or an access point set up in "extender" mode.

Which is easier to do and gives the better result?

They're both relatively easy to do but I have had some issues using wds bridge mode from a router to an AP, whereas AP - AP was fine.

If your only usage is the connection to the camera it's probably worth trying repeater mode

See here https://www.draytek.co.uk/support/guides/kb-range-extender

(other guides are probably available)

Other makes of AP usually include guides for setting them up in repeater mode - check out specs on the websites