Synergy VS Multibox

From the posts I have been reading lately it seems more people use synergy than multibox. Is there something that synergy can do that multibox cant?

I started right off with multibox and I have no complaints. I love that you can choose which keys to broadcast and i hear synergy cant do that. So why use synergy?

Which do you use?

i use synergy, becouse i've used it a LOT before when i was just using 2 pc's (1 for wow, the other for movies,websites,....)
there IS a synergy version WITH broadcasting..
the mouse part doesn't work but i've been dualboxing all day and it went great