good luck, you'll be working with my dad 😀
The riding is good in places, but a bit scattered.
There are some pretty hardcore riders in the Marine Lab so sniff them out and you'll get some good tips.
Also bear in mind that there's at least one world cup level DH-er living in Benderloch (just north of Oban) who trains and rides on Beinn Lora and Barcaldine forest, the Beinn Lora trails in particular are pretty nice (and I built some of them 😉 )
I also know the local club have built some very tasty singletrack sections in Barcaldine Forest, although unfortunately its still predominantly fire road.
The hills behind Oban have got some little trails criss-crossing them, but I needed the owner of the LBS to show me them and its since shut down I hear.
South of Oban there are also nice trails around Scammadale but they are a little awkward to make a loop out of.
Edit: Kerrera Island, in the bay, has a great loop around it, I think Singletrack actually did an article on it a while ago…