SL. ML would probably not even install on the 2007 MBP, and even if it does, the 2007 MBP does not even meet the minimum system requirements, so it would likely run like crap.
My bad, the mid 2007 does meet the requirements.. barely.
You may need to add SSD and 6 GB RAM, but it functions well with ML. Just don't let it overheat or you could frap the logic board, like I did 3 days ago when working with video.
I have a mid/late 2007 MBP and I installed Intel 320 SSD before I installed ML, it seems run very decent speed. I am happy anyway. I should have spend more time with SL to see the difference.