Suggestion required for buying ram sticks

I have four slots on my motherboard for RAM and I want 4GB of RAM which I would be running on Windows Vista 64bit system. Here I am bit confused as to should I purchase 4 sticks of 1GB RAM or should I go for 2 sticks of 2GB. Let me tell you something that this is my new build and I have no idea which one would be better and why and would appreciate if somebody will help me.

Performance wise 4 x 1GB would be better as it might get increased but it is hardly noticeable. Whereas, cost wise 2 x 2GB is better because 2GB sticks are cheaper than 1GB.

Agreed to Archibald and also you can upgrade your system whenever you want but adding some more sticks to your empty slots and thus enjoy extra ram.