There's so many classic ones. It really depends on my mood of day.
Bad Luck Brian never gets old.
Scumbag Steve is overdone but there's a few great ones.
Successful Black Man Meme was funny but got repetitive.
Skeptical Third World Boy is great.
Unsure Fry (Futurama) always has good ones.
Nic Cage "You Don't Say" meme is great.
Neil Tyson "We Got a Badass" is great.
I've seen less and less of the Jackie Chan imposibru, and Yao Ming meme. The Patrick Stewart Why The F--- meme is getting overdone IMO.
Basically I just go on 9gag and I never fail to get a laugh.