Best C Compiler?

What is THE BEST (or your favorite) C compiler?

1. gcc (GNU C Compiler)
2. pcc (Portable C Compiler)
3. tcc (Tiny C Compiler)
4. dmc (Digital Mars C compiler)
5. icc (Intel C Compiler)
6. lcc (Local/Little C Compiler)
7. other (please specify)

Explain why it is your favorite or THE BEST or why other choice(s) suck.

I was told that this example of include-guards:

/* somefile.h */

#ifndef _SOMEFILE_H_
#define _SOMEFILE_H_

/* put your declarations and stuff here as usual */

#endif

is bad because it "invades the reserved namespace for identifiers", but that it would be perfectly fine if I removed the leading underscore.

I don't quote understand how it's harmful to the namespace with the leading _, or how removing it will somehow be better.  Can someone explain?