I use the same as everyone, taught it in training class. "Down" to lay down, "Sit" to sit and "Off" to get him to stop jumping up on anything/anyone, all very different commands and you should only ever have to say them once according to my trainer. Granted at first it may take a while for them to do the command if you're used to repeating yourself, but they do hear it the first time. I usually give my pup a nudge if he takes his time, such as "Down" and if I get no response I'll follow it up with anything really such as "Ahem." or "Excuse me" etc. Just some good tips I've gotten from training so far.

I don't think I use any two syllable commands at all.