I happened to write an article on this topic not long ago. Here is an illustration from that article showing dual triple blocks:
The cross reeving almost always works out better, imho. Also, having the tail come out the center sheave of the block keeps the load even when that line is not pulled straight toward the second block as shown in this sketch. This prevents sideways twist which can cause additional friction. You will get some rotation if you do that, but it will not tilt the blocks sideways and the sheaves will stay lined up.
The article is here:
http://l-36.com/blocks_mechanical_advantage.php