FG is what I'm familiar with, it supports Traveller, and it doesn't demand I use a web browser I won't use. Its devs don't seem to care about Apple Silicon, though, which may mean my RPGing days will come to an end the day I upgrade my desktop.
Typically run Foundry though I’ve used Roll20 in the past and Fantasy Grounds.
I’m considering giving Owlbear Rodea a try this year. I’m looking for something light weight for just maps, images, and tokens. Bonus if I can draw on it like a white board.
I like that only the GM needs to pay for a copy and its a one and done payment, no subscriptions. Its not difficult to host your game locally on your own machine either. It has pretty good functionality out of the box and with community modules its really elevated.
I tried Fantasy Grounds (it felt too dated to me) and Roll20 (absolutely bare bones), granted it was several years ago that I used either so they may have improved.
Fantasy Grounds. I like it generally, but mostly it is a sunk cost thing. I just have so much in FG I can't justify buying copies for Foundry or whatever.
While Roll20 is what I use for most games, and that's what I voted for, I also found that PlayingCards.io Virtual Tabletop is a good one to use for those rare games that use playing cards instead of dice. I use that for Princess Wing.
Maptool. Doesn't cost anything but the time to learn it (which to the degree I care I've mostly already done), and not dependent on someone else's server.