All of the above mentioned have pros and cons, so have a good think about what type of aircraft you want to fly and what you want to do with it.
From what I’ve learned in the last couple of years:
- FSX is old, but has tons of extras (partly because it’s old). If you want to practice air traffic knowledge in a civilian, seems to have the edge. Only supports VR with an aftermarket tool (to my knowledge. All the rest include native VR support)
- Xplane 11. Would be my choice for a civilian simulator. Comes with a reasonable starting number of aircraft and helicopters. Looks good. Picture it as being FSX mk2. The only real downsides being that because it’s fairly new, there’s no the level of mods available for it
- IL2. Best for WW2 combat and has recently added WW1 as an option. Doesn’t include any jets or helicopters. Doesn’t feel as real to me as DCS because the cockpits don’t have the equivalent of the “hi fidelity” modelling that DCS has, which allow you to click inside the cockpit, which feels very natural. Runs really well in VR
- DCS. Includes 4 WW2 aircraft, 4 helicopters, and a reasonable number of jets (e.g. Harrier, A10, F18). No commercial aircraft. For me, the flight models and feel of the aircraft feel more real than any of the others. The Huey is recognised by many as probably the most accurate helicopter simulation available. You have the option of standard or high fidelity models. There’s 7 standard ones bundled within the Flaming Cliffs 3 bundle (F15, A10a, Su27 etc). The FC3 aircraft are basically very similar to the model level of IL2. They share the same high quality flight model as other DCS aircraft, but controls are much simplified and you can’t click on cockpit controls. You’ll probably conduct less air combat in DCS as you really need to learn how to fly the aircraft, typically they’re MUCH more complex than most sims make them out to be. Unfortunately, not very well optimised and needs a serious system to run it well, particularly in VR. Vulkan support is coming, which should help. As mentioned, you can download and test DCS with the 2 free aircraft (P51 and Su25T). Give them a go.
- Warthunder. Arcade style game. If all you want is straight combat in a small map, it’s perfect. Includes early WW2 to early jets and now some helicopters. Flight models are pretty simple. Runs really well in VR.