We just get whatever toothpaste looks decent at Petco. We have mint flavor right now; before that we had peanut butter. Sadie has only ever had the mint, but Quincy has had both, and seemed to like them both equally. I will say that the mint is far more palatable for DH and me to use. Smearing the peanut butter scented one all over their teeth is kind of gross.
As for the toothbrush, we have both the regular kind with the long handle, and the finger kind, and we have much better luck with the finger kind. Plus I like being able to feel which teeth I'm brushing so I know when I've got them all.
Tips - just get them used to it before you head in. We let them sniff and lick the brush, put a little toothpaste on it and let them lick it off, etc. We only brush probably once a month, so letting them play around with it for a few minutes to let the novelty wear off makes it easier for us to get in there and get some brushing done. I guess we should probably do it more often, both for dental hygiene, and so the equipment isn't a rare fun thing each time, but we don't. Oh well. lol.
Part of our ongoing dog care is to touch their paws, butt, pee pee area (lol), and lift their...lips, I guess?...and touch their teeth and gums. It keeps them used to it so they don't mind when the vet does it. I think it makes brushing easier too.