It's a personal preference, there is no correct answer here. I prefer lump myself, just so you know where I'm coming from. It definitely burns cleaner and hotter, but in general, I do not agree that lump burns longer. Some brands of lump can burn for quite a while, but Kingsford briquettes can burn for a very long time for a lot less money.
The reason I like lump is because of the reduced ash, and faster response to air adjustments. I also like lump better because it is just wood, that's it, nothing else. In fact, some lump even produces a smoky flavor in food.
Stay away from Cowboy, and tell your friend that uses Cowboy that they should do themselves a favor and start looking at other brands of lump. Cowboy is truly that bad.
Pretty much anyone, anywhere can find Royal Oak lump somewhere, many get it from Wal-Mart. Wicked Good is basically top of the line lump. It burns hot, and burns for a long time. It is pretty pricey though, but worth it as long as you can afford it. Otherwise you should check out the Royal Oak.
The 100% hardwood briquettes mentioned above also work, but I still prefer lump. It is truly personal preference, there is no one correct answer or else we would all be doing it that one way.