I think the second shot at 16 is one of a kind. The quarry gives the hole a look that is completely unique. While the land is wild at 18, there are still other holes like it. Not so with 16.
I think the internal contours of the 16th green are more interesting. I probably did not get a close enough look at 18, but the green did not appear nearly as interesting as the 16th. The hole plays completely differently depending on the pin position.
I love the quirky nature of the 16th. It gives the hole a charm that the 18th does not possess. The string of bunkers to the right the green is very neat. It fits into Merion's collection of odd but fun features.
Finally, I like that the 16th has an out for the weaker player. A short hitter can play around the quarry to the right and find the green easily in three shots. The only option for a short hitter on 18 is Paul Runyan's strategy of chipping down to the forward tee. As much as I love Little Poison, I do not think his option makes the hole less unreasonable for short hitters.
I appreciate that 16 is not strategic off the tee. It does not present the tradeoffs and decisions that holes like 5, 7, 10, or 15 certainly do. Yet for the reasons above, I prefer it to the closing hole.