silver bullet gun oil (SBGO) is a favorite on here.
pretty much whatever you have, they don't need very much. Just about any kind will work fine, even dry lube.
I use homebrewed oil, synthetic motor oil and oil stabilizer with a touch of bore solvent.
also I use a barber brush (two actually, one dry that never touches oil and one for oiling) to apply a nice even coat over whatever I need on the gun.