What oil are you guys using?

With uncertainty of the last time the oil was changed before I bought it, it's one of the items at the top of my list. I did manage to download the manual but it only says Honda 4 stroke SAE 10W40 (85 200S). Since I'm new to the Honda ATCs is there a recommended oil from the group or do you just use whatever is handy (of the right viscosity)? Also, how much fluid does it take? Thanks.