Which virtual airlines are some of the top ones these days?
The best thing to do is consider what it is you wish to fly and in what region, then look at the VATSIM VA list [https://my.vatsim.net/virtual-airlines] and seek out the ones you think are suitable for you. IF there are multiple that fit your desires, open up their home page and look at Roster (is it fairly big), PIREPs (are the members active), policies (can I fly what and where I desire).
I fly primarily for Southwest Virtual (in the USA). Loads of support and training options. They will help you obtain your VATSIM ratings via numerous training activities and events. The downside is that your flights only “count” (towards your rank with the virtual airline) when you fly real-world Southwest Airlines flight schedules (with a Boeing 737, of course). You can choose to fly routes in real-time, or whenever it suits you. Group flight events are held one or more times a month. I only participated once (and it was quite some time ago). The profanity spoken by a few of the participants really put me off – maybe this has changed since then, though. Oh, Southwest Virtual’s client software (currently LUVCARS5) is very stable and almost never crashes, which would result in your flight not counting towards you rank advancement. If for whatever reason LUVCARS doesn’t record your flight, the VA will accept “proof” of your flight via a Volanta recording, assuming you’re tracking your flight that way (which presumes your computer system can handle the CPU processing overhead the Volanta software puts on your computer).
Also, a friend of mine runs an American Airlines VA. They require two flights per month to remain in good standing. Lots of group flights and the owner, Pat, is heavily involved. Really nice guy, all the way around. To my knowledge, his VA does not put any restrictions (at all) on where you can fly, as long as you connect to VATSIM with an “AAL” callsign and with an aircraft type flown by real airline. Look for them at “JoinAVA” on Discord.
I am flying vEZY these days. It is important you understand how they work. E.g. some operate by timeslots and real connections - great to give the real world feeling but restrictive regarding locations and opportunities. Works best when you select a virtual major player e.g. virtual DLH. The rules for qualifications for the flights also differ e.g. for vEZY you need to pay attention to livery and plane type, while vDLH is more liberal. Most virtual airlines use qualifying limits on FPM at landing; vEZY has a series of other points of attention (flaps, engines, …). The ACARS tool that follows your flight might be good or not so good (I like Pegasus, the vEZY one). Etc. Read carefully what is expected both in what you are allowed to fly and how a flight qualifies and select what feels best. Check what else spices the virtual airline up (training, discord activity, events, …)
Really depends on what you are looking for. There are casual VA’s and hyper realistic VA’s
Also like others mentioned pick a region you want to fly in.
You can check out Skybus Virtual it’s a hyper realistic VA so it’s not for everyone.
another hyper VA I know of is Coastal Airways
If you are looking for a more casual but authentic experience hands down Southwest Virtual.
Good luck in your search