The game runs on a client/server architecture currently setup for TCP, and the client code was built in AS3 to be web based.

What we're running into is 3 problems for the client.

1. AS3 has no hardware acceleration so we are having some issues with slowdown when implementing some features
2. TCP is really frustrating for a sidescroller when you're talking with a server. I'm having a heck of a time with the interpolation/extrapolation to make everyone else look smooth while minimizing lag. I would much rather be able to use UDP and throw in something similar to the age old Quake interpolation/extrapolation.
3. No right click

I work professionally with C#, and I did all my University (almost 2 years ago) with Java. Java really appeals to me because of the compatability while C# appeals to me because I've heard so much good about XNA and I love visual studio.

For a Client/Server based MMOish sidescroller in your opinion should I stick with AS3 and the TCP protocol, or should I abandon some of my audience, ramp up the graphics and hit C#, or journey back to the land of Java.

Thanks :D