For learning or formal development of C#, there are only two best IDE for choice at present: either the 10+ GB size of Visual Studio or SharpDevelop with only 10+ MB file size. The latter is an open-source IDE with layout similar to IDEA for Java and high flexibility & extensibility, which lets a user find everything new and fresh. It never wants to be an IDE that tries to support everything as Eclipse. Instead, it just gives you an interface, and you can do all the rest by yourself.