short answer:
for spool bearings i use td-z oil or hot sauce (any real fast/low viscosity) oil
all others: a light grease (abu silicoat, reelbutter, hot sauce grease, lithium)

longer answer:

this is what i do for relubing stock bearings:

for spool bearings (spool shaft and side plate....any bearing the spool spins on):
i remove the bearing and run it in the ultrasonic in a glass vial of acetone for a few cycles. if you dont have an ultrasonic, just let them soak for a few hours in acetone. then let the bearings dry completely. next, you want to check the health of the bearing by placing it on something and giving it a few spins. listen for any irregularities or rough sounds, if the bearing is damaged....REPLACE it! after determining that the bearing is in good shape, i lay them on thier side a put a few very small drops of td-z oil or hot sauce on each. then spin the bearing a bit to work in the oil. i always use a very thin oil on spool bearings.

for other reel bearings (drive shaft/pinion/ ect.....):
soak or ultrasonic the bearings/check the health of the bearings as described above. if the bearings are good, i remove the shields and add a thin layer of grease to each side(or, you can buy a bearing greaser where you dont have to remove the shields) then replace the shields and retainers and spin the bearings a bit to work the grease in. be very careful with the bearings while the shields are off as it is possible with some bearings to push the cage loose.