By taking out the outliers Coors Field and the Ballpark in Arlington, and all Cubs games since they tend to be very high or low in summer, I got an 8.5 leaning to the over in the NL and a 9.5 leaning very slightly to the under in the AL.
I know most people disagree, but I love the DH. Makes for better game aesthetically because who really knows what a manager is thinking for one and for two I just hate seeing a dead out that usually bunts or flails at a couple of breaking balls. More greedily I find the AL far more predictable for totals.
I am not quite certain why, but I have my guesses at it. If I had to state the one I believe is most important it is the very strategy of the AL managers and how they are far more inclined to go for the big inning, which then forces managers when it happens to go into pathetic bullpens. The converse is the NL with fewer big innings and lots more playing for ties and one-run leads can create almost lucky spots where the exposure of the pen can hinge on something as simple as a bad pitch call by the umpire. He might call a walk, which leads to a pinch hitter, which leads to a run scoring opportunity that might not have happened. Then the pitcher is out and the pen comes in and can swing a games momentum as well, sometimes good and sometimes bad. I really tend to be very conservative with the NL using totals and I suspect the DH rule has something to do with it.