Definitely 2 x 8 GB. 2 x 16 GB would be preferable as new games will start to take advantage of it soon.
You always wan to run your RAM in Dual Channel. You will have a perceivable difference in performance. Triple and Quad channel exist but only if your motherboard and CPU are configured for it....though they don't help much over Dual Channel anyway.
Massimus - "Trump already has democrat support."