Selecting a best RPG session of the past year is tough -- which is actually a good sign when I think about it. I had a great time playing a Gencon game with two friends from junior high (whom I have not played with together in over 20 years). I had fun with a brief online campaign (about 5 sessions) and an online session run by Darcy Ross based on Into the Night for Numenera. The games I ran at Gencon were fun. However, the most fun I have had in a session over the past year was a game at NTRPGcon.
I got to play an old school Paranoia game with one of those friends from junior high. I don't even know which edition it was (but it was clearly based on some old books -- since we saw the actual books). Friend computer was failing, alpha complex was breaking down, and we had to go find a replacement part. This sent us into a twisted version of Disneyland dominated by insane mutants and even "insaner" animatronic robots (think the Country Bear Jamboree).
I took my lead from the instruction that happiness was mandatory in alpha complex. That started my friend and I riffing. He ended up spending most of his time asking for the monkey companion he was promised. I was looking for any sign of treachery -- usually in the form of an indication of less than complete bliss. In the end, I loved it.
What I learned most from this was how subjective the enjoyment was and how little it depended on the game system. We randomly generated mutant powers -- none of which any of us ever used (I think). We choose all of our character skills based on a poor explanation of the rules (resulting in BADLY mismanaged characters). All of this and I still had a blast.
My friend enjoyed the game - but less so. He had previously played Paranoia and enjoyed the PvP component. We cycled through clones but mostly due to external opposition. He and I started some PvP early on but the GM and other player (there was only one other, long story) did not seem to contribute so we just moved on to other styles of play.
The game system was either remarkably robust to a poor understanding of the rules and limited player interaction or the system truly did not matter. Most importantly, I just have fond memories of the whole experience. This reinforced my view that system matters a lot less than the disposition of the players.