The DM I play with uses 3.5—he has so many of the books that he lines the coffee table with the spares so that the dice don’t mark the table. Piled up, the books would probably go higher than a metre (3’6”). I, on the other hand, game using printed PDFs and a digested, 20-page, home-ruled version of Labyrinth Lord.
I like the coherency of the d20 system, and the fact that it has so many options. However, I think that the plethora of options can be daunting, especially when you’re playing with new players (none of my players have ever played before), and for a beginning DM (i.e. me). So, in that respect, LL is a better choice (and also, it’s free, which is a huge bonus).
The other advantage is that I get to use Dyson Logos’ truly awesome hand-crafted character sheets.