I have used mainly what I could get in my locale.
Started with royal Oak, great middle of the road lump, has some wierd pieces in in it sometimes, not a real uniform mix. Good flavor, decent price.
Moved on to big green egg, seemed to be a bit higher quality than the above. More unform peices (size wise). Good flavor, a bit more spendy than Royal Oak.
recently I am on Lazazri mesquite. Decent deal buying 40# bags at my local cash and carry. Better flavor than big green egg and royal oak. Looks like it actually comes from trees as opposed to the other 3 I've tried (big green egg, royal oak and cowboy).
I'm not even going to comment on cowboy lump
, I'd rather my lump peices be at least the size of briquettes, this stuff falls through the grate in my chimney.
All in all I can't tell too much difference between decent lump as far as flavor goes. I can tell some difference when I get a wiff as I first fire it up. The lazzari wins in this catagory for me. It also takes the win for most natural wood, this may not be important to you, but I like to know as much as I can about the origin of the food I stick in my body (or the charcoal it's cooked on in this case).
Anton