what would better improve a notebook's performance, a 4GB DDR3 or a 100GB SSD [on hold]

what would better improve a notebook's performance, a 4GB DDR3 or a 100GB
SSD [on hold]

I am using thinkpad E430 with win8 as my primary workstation. The
notebooks bears lots of computing and programming tasks and I need to
alternate between vmware guest os(linux) and my host win8 quite often. As
a result, I am very concerned about the speed of the computer(especially
in VMWare).
I currently have a 4GB RAM and a 500GB HDD, but I can still feel
significant latency when alternating working os in VMWare, and hence want
to invest more in the hardware. That said, which of the two options,
adding a 4GB DDR3 or a 100GB SSD, would better facilitate the notebook in
my case? Thanks