My favourite depends on mood and varies from the gals of Bubblegum Crisis to KOS-MOS from the Xenosaga game/anime/artbooks. Today, it's KOS-MOS.
Image shows Shion cosplaying as KOS-MOS. Shion is one of the two principal creators of KOS-MOS. The set of cut-scene videos compiled by Studio Onegai (into a coherent set of episodes) is the best version of the Xenosaga story. Studio Onegai's founder (Jessica Merriman) went on to create MOMOCON which is a large free-admission convention named after MOMO from Xenosaga. A scanlated doujin is available at
http://www.mediafire.com/?tywtt5z02iw for those who are new to xenosaga doujinshi.
http://en.wikipedia.org/wiki/Momocon 
