The best way is to agree on a standard with your colleagues, and stick to it. It doesn't absolutely have to be the method that would work best for everyone, just agreeing on one method is more important than which method you actually agree on.
What we chose for our code standard is to use _ as prefix for member variables. One of the reasons was that it makes it easy to find the local variables in the intellisense.
Before we agreed on that standard I used another one. I didn't use any prefix at all, and wrote this.memberVariable in the code to show that I was using a member variable.
With the property shorthand in C# 3, I find that I use a lot less explicit member variables.
