being as i have multiple pairs of JOs/Bullets....
center without a question, mounting back is BS unless you are riding pow, hell i even put demo bidings on my race skis and moved em forwards so im only .5 back from center...and i have been skiing better. You have more tail so when i get backseat im not totally fucked, they ski shorter which is really nice for slalom, and i feel like i get a more even rebound off the skis....but hey its all personal preference