Jock,
OK, if you're at the North end then try the following
Mishnish Lochs
Head towards Dervaig from Tob and about 3 miles along the road on the LHS you will find the Mishnish Lochs. 3 Lochs and all three have boats on them. Managed by Tob Angling Association and permits from Brown's Ironmungors. This a fly only water (like most on Mull), lochs are stocked with fingerling trout every 3 years and some grow on to a good size (had a 4lber last year on the middle loch).
Aros Loch
Rainbow water and bait and spinning allowed. This fish farm on this loch is defunct now and I don't see may fish it anymore. Wouldn't bother.
Loch Frisa
You're best bet (fly, spin, bait). Big water (biggest on Mull) 4 miles long and very deep. Good size brownies, also Ferox and Charr (apparently). Local farmer (John McDowell Lettermore) I know hires his boat on this loch. No other options for a boat but decent bank fishing at the south end. Had a big release of salmon smolts last year so I don't know as yet what that has done to the fishing. Can be unbelievably good.
Loch Torr
Small loch after the Mishnish lochs, great for fly beginners lots of wee free rising trout. My daughter had 10 in an hour
last year.
River Bellart
Can spin and bait fish here but needs rain. If no rain suggest going to the estuary as the salmon and seatrout (not so many now) sit an wait for water from June onwards. No brownies.
River Aros
Same deal as the Bellart but bigger and has a number of named pools. Upper reaches fly only.
Loch and River Ba
Salmon and seatrout loch expensive and again needs loads of rain, river is cheaper but very short
There are a number of lochs in the hills if you fancy a wee hike, if your spin/bait preferred I would stick with Frisa
Gordon