There are currently several options for online MP depending on your flightsim platform. In terms of number of users in the MS FSX descendancy, FSX-Steam Edition leads the pack followed by FSX boxed, then P3D based on its default MP.
For voice comms, Team Speak 3 is the most popular among gamers (flightsimmers included) and some use the freeware Discord. You can look up who's online in TS3 using TSViewer. For cross-platform MP, I have tried using DAFSIM (server/client-based, supports FSX boxed/FSX-SE, P3D & XP, stable, bit complicated to set-up, mostly European VAs use it), FSHost (client/server based, supports FS2002/FS2004, FSXboxed, FSX-SE & P3D, easy to set up, occasionally jittery/laggy depending on latency/connection) and JoinFS (peer-to-peer, supports 3 platforms except XP, lightweight to setup, newly developed). There's also FSOpen server for FSX boxed legacy MP replacement of the old GameSpy. There may be others. Just Google these up. There's usually related info online.
By the way, I read a while back in AVSIM that the FSCloud does not support choppers yet, can anybody confirm if this is still the case with its latest version? I can't seem to find newer info about it. Thanks!