AOPA's is pretty nice and has improvements added often, as they tweak it..... BUT even after several complaints/emails, they still don't have the CT listed in their aircraft database! The FAA designator "FDCT" is not recognized. I've pointed this out to them, since the first day of testing the new system, and they said they would fix it..... oh well, 6 months, not yet.
Also, you can't submit DVFR flight plans through the AOPA system.
I use weathermeister.com the most.
I've played around with fltplan.com and aeroplanner.com and gearsdown.com (which now seems to be down). Skyvector.com has added some flight planning. Flyagogo.net has charts & weather, but no planning.
tim
275+ hours of CT flying fun!