The stamped one is supposed to spin freely, it cuts down on the friction. As for which last's longer? I've never seen either wear out in any engine I've torn down. Both seem to last forever.
Just wanted to say thanks for all the responses on this thread. There is a lot of good info in this thread for others to reference in the future who have the same challenge I did. I installed the 2 piece eccentric and buttoned up the rest of the engine from the oil pan to the intake this weekend. Can't wait to drop it in and fire her up, but still lots of other details to get to first...