This is a tough one, mainly because I use a wide range of emotes. When I first thought about it, I came up with these...
/point, followed by a /laugh
Before Real ID was introduced, emotes were the main way I could communicate to my Horde friends if I was running around on Krinkal. If I was on Vent and they weren't, /talk was my way of telling them to get on Vent, because I was bored and wanted to chat.
When running around Dalaran (which seems to be not just my past time but a large amount of level 80's on Argent Dawn as well) I'll bump into people I know - long time friends, new acquantances, guildies or people I know on a different faction. Depending on who they are and how well I know them, I use a different emote. It's like a social heirarchy of emotes, with the people I've known the longest, or see as close-close friends get a /love, where-as people I dont know much get a /poke. People in the middle get /hug or /tickle and if I'm bored, I'll /dance with anyone! (I know, I'm such a slut...)
/point followed by /laugh is my long winded way of going "lol" but as an Undead, it's great to watch them /point, which for anyone who's never played an UD male, looks like you're calling them out for a fight followed by a /laugh which is the complete opposite, as his ribcage collapses and you can just imagine him weezing his little, lifeless lungs out in hysterics.
However, I'd missed one of the list and it's the one I like the most - /silly. I could literally spend an entire 10 minute raid break just spamming it, laughing at the bad puns, daft jokes or pop-culture references that all the different races have.
Now you know mine, what's your favourite emote?