I have spent a lot of money on kit, but only practice makes you faster. The extra kit adds immersion, which oddly enough can slow you down. When I got the 3dof motion in VR, the first time I crashed it threw me about quite a lot, which led to me being more careful and ultimately a little slower.
The short answer to which game/sim is drive the one you prefer, but there lots of good options already mentioned.
I use PC2 for a free and fun time trial competition which is run at
www.stoopidchallenges.com. Requires an app to run to collect data and telemetry, windows and IOS versions available, started out on Pistonheads forum. Usually 20-30 people running weekly time trials cross platform.
ATS/ETS2 for chilling and easy driving fun, surprisingly addictive.
iRacing - recently restarted/resubbed, got up to a C class licence and stalled now because every race requires me to purchase more tracks and cars...I'll probably end up getting it at some point. It's simply the best place to find a race with their online matching system.
Others:
AMS2 - still a work in progress, in VR I can't get it looking as good as PC2 for some reason. Some interesting and different content to play with.
AC - lots of mods and content, never really got to grips with it fully and again can't get it looking great in VR
ACC - haven't tried it for a while as it just wouldn't run properly in VR, lots of good noises around so it must drive nicely.
F1 - good on screen gaming for when I get fed up of VR (not very often)
LFS - Still installed, but I've rarely played it recently, good fun and runs on potato systems
RF2 - I've tried really hard to enjoy as it drives really nicely, but it's such an old game/sim, it's just not optimised for VR and the UI is appalling. Keep going back and trying it hoping they can bring it up to date.