imho, ICC is the gold standard. You can get at least a simul with a master almost everyday. The GM commentary is incredible for live tournaments, and things like ICC's Game of the Week from GM Joel Benjamin are unmatched.
If you haven't yet taken a look at lichess give it a shot, it's wonderfully elegant and well-done project and there is a lot of great talent that plays there as well as wonderful features such as lichess tv, coaching, analysis and puzzles which are all free -- and there's no ads, the UX design is very click, too!
Edit: I'm not a Master and don't need that level of competitiveness, but on lichess TV I am always seeing Masters playing there.
Edit: The ICC app does seem to have Chess960. However I couldn't tell where my offer went in free mode, and the UI was filled with stuff I couldn't use. Lichess's UX seems slicker. In particular:
a) When you open the app you get a problem. Solve it and you get another, and another and another.
b) You can ask for computer analysis after a game.
I'll always remember BlitzIn fondly (it was the first CLI I used, before I even knew what that was) but ICC's glory days were the late 90s and early 00s.