1st - Sector 3 for me. Racerooom has had some excellent updates and I have so much fun playing DTM'92's online on VTM Nordschleife that i now play Raceroom more than my other Sims (AC,ACC,AMS,RF2,DR). They also added great content (WTCR 2018, GT4) and continue to improve all aspects of the game, i just hope they update the engine at some point so we can have dynamic weather. As much as i enjoy this great game, it has its flaws, lets hope Sector 3 will address some of these in 2019.
2nd - Reiza - AMS was quite the find for me in 2018. Great fun to be had in their openwheelers (something i dont usually enjoy). Serious Sim with some new content added recently. I just hope they add the Nordschleife at some point and maybe a few European cars. I bought the season pass on sale to support these guys. Hopefully they continue to add to the game and the servers fill up a bit more, a little sparse of players...
Great game though, i hope they build upon their unusual car and track roster but also add some more familiar European cars/tracks too. I'll be keeping an eye on this team and AMS in the New Year.
3rd - S397 - rFactor 2 . The GT content was a welcome and excellent addition. Seems to be renewed vigor behind the development of this game (Most welcome and needed). Many people swear by this game as being one of the best sims. While i dont have much play time in it, i have seen flashes of the magic people speak of, but there are areas of the game that still need vast improvement. (UI, Quality of content). Momentum appears to be with this title, lets hope it will continue.
4th - Kunos - ACC This game was released close to my birthday so i treated myself to another Sim. I was very excited by what Kunos would do next after being a big fan of AC. It would be unfair to be over critical of ACC given its still EA, but i dont share in some of the enthusiasm from my initial impressions. I didnt realise how much i relied on Head Tracking/Track-IR until i fired up ACC only to be devastated to find out it isn't yet implemented, nor is it listed anywhere in the games road map. I am sure it will be added at some point and I will play the Sim again, but until then i have shelved it. The graphics really were underwhelming too, but again, its still in EA and Kunos of course have delivered the goods before with AC. Lets hope they find an extra gear in the New Year and make ACC the game it should be.
* I have yet to try iRacing. Perhaps 2019 will be the year I can overcome the paywall and justify such expenditure. If the aforementioned studios continue to develop and improve their title's, I might have to wait another year for iRacing!