Azorius, Dimir, Rakdos, Gruul, Selesnya, Orzhov, Izzet, Golgari, Boros, and Simic.
Esper, Grixis, Jund, Naya, and Bant.
Jeskai, Sultai, Mardu, Temur, and Abzan.
I've played them all at one time or another. Think Sultai and it's derivatives (Dimir, Golgari, and Simic) are my preferences; my most entertaining combinations have been sourced from there.
My advice: work you way around the pie. Try all the colors, even the combinations that you think you can't play. In doing so, you'll learn how they work, and gain a better understanding for what your opponent might be plotting.