LM Bora Bora. Probably because I was there for 4 free nights on SPG promo in 2009 (stay 7 nights at any LM, get 4 nights free at any LM). I was newly minted Platinum (which I strived for just for this trip, 25 stays, 27 nights I think) and was upgraded to OTWB, second from the end. Weather was crappy most of the time, but that was such an amazing trip/upgrade, it sealed my love affair with SPG. Before that I was Marriott/Hilton loyal but never felt the love like I did from SPG on that trip.
^
Look at me now. 100+ nights/yr. Lifetime Plat!