My i7 920 build is currently running 3gb of ram, and I can get another 6gb for 65 bucks. I think this might be the time to upgrade the ram before the prices go up again. However, I have seen mixed results going from 3gb -> 6gb, but upgrading to an SSD seems to always improve performance.
I would like some opinions on what would be the better upgrade
It really depends on how much memory you need, which varies from person to person based on what programs they run and how much stuff they've got open at the same time. Adding RAM beyond 3GB might be totally useless for one person, and a tremendous improvement for someone else.
Use Task Manager (Ctrl+Shift+Esc) and have a look at your Memory graph when you've got the biggest load on your system. If it's less than 2.5GB or so, then adding memory won't help all that much other than giving you more space for disk caching.
If you do decide that you'd benefit from more memory then make sure you have a 64-bit operating system, otherwise you won't actually be able to use it.