J.J.'s Advice / Avis de J.J.
Even just watching a couple of videos a month will out you over 500mb. I would definitely go with 3GB.
jon_mac_usa_007
Assuming you are referring to your monthly data use, 500 mb is a half a gb, so 3 gb is 6 times more. 500 mb is a tiny amount of data usage, so certainly get the 3 gb of data plan.
SRΛSC
Only you would know this, by experimenting. Try out the 500MB & see if you could manage, if not then change.