Considering the quality of the question, "More" is the generic solution. In most cases if an average PC is struggling due to RAM it is because there is not enough of it. Today when purchasing RAM one can have basic 2 options:
a) 16GB of RAM of generic type
b) 8 GB of much more expensive faster RAM
Of course other configs also exist but I would say this is most common current dilemma when facing faster RAM.
The faster RAM often does nothing in day to day work but 16GB will benefit more in the long term...
I went for 16Gb of faster RAM, but that is because I could afford to. If they asked me more or faster RAM, in general more is the answer.
8 Gigs is enough to run most games, but I see more and more issues creeping up when not having 16GB of RAM. 16Gb enables caching of programs, textures etc and will give generally greater benefit than half the amount of faster RAM in most situations. Of course one could find some borderline case when using photoshop where only little RAM is needed to render something (unlikely) where it would benefit more to get the faster version of the RAM. Good luck with that argument though.