This is one of those things that people tend to debate nearly endlessly, and I have yet to really hear a definitive answer.  The fact is, each of the colors in the game has its advantages.  I have never been a fan of single color decks.  I find them boring.  My chosen decks of Magic Cards are usually two or three colors.  My favorite color combos are black and white, and blue and white.  Even when I have a black and white deck, I like to add some blue in if possible because I just hate to not have the ability to drop a quick counter-spell.