I log almost all my plays on RPGGeek, with a short session report in the weekly "How did your RPG session(s) go this week?" threads. This means I can offer a detailed count!
Pathfinder: 12 sessions, because of nathreee's Guildfinder campaign. We ended the campaign, and I think that may have been the last Pathfinder I'll ever play.
Dungeon World: 10 sessions. This started out with a campaign streamed through Twitch, now defunct. I am running a campaign for friends with DW and I've done some one-shots.
The Sprawl: 9 sessions. This was the (again, defunct) "Ashes to Ashes, Chrome to Rust" campaign which was also streamed live on Twitch. Of all the new-to-me games I've played, The Sprawl is my favourite, hands down. I'm really sad that the campaign ended, but that's how these things go.
The One Ring: 8 sessions. I ran two friends through Tales from Wilderland, but in the end there was not enough momentum to continue and I ended the campaign. 2 hours every 2 weeks is too little.
D&D fifth edition: 5 sessions. Some one-shots, but also the start of nathreee's Zilversluizen campaign.
Star Wars: Age of Rebellion: 4 sessions. This is a mini-campaign, and we expect to go on for two more sessions. I like the system more than I thought, and the scenario is fun.
I was surprised to see Pathfinder take the top spot: it is by no means my favourite RPG. But pretty much everybody I know has converted to D&D5 or other things, so...
If we're looking at game system families, then the Apocalypse World Enigine comes out on top with 19 sessions, whereas the D20 family (Pathfinder and D&D) have 17 sessions. I must say that the AWE is my discovery of the last year. The focus on 'the fiction' and both the versatility of the system and the niche protection of the playbooks really 'click' with me.