Here comes the Gemini twin, looking for the brother of the oil...
Actually I don't have a fav one, and I answered just on the base of the alignment I feel.
I probably feel equally aligned with Mars as well, and with Jupiter and Pluto. But if I had to put my "personality" undera Planet Type, I think it had to be Mercury.
Mercury is quick (only slower than the Moon), is comunicative, dynamic, outwardly oriented, and his Geminian qualitie describe me quite well.
Also, in less modern traditions Mercury was exalted in Scorpio, sign of my rising, and to which I am very bound as well; the Scorpio qualities complete the Geminian ones very well in my opinion, and highten some features alrady present in Gemini, like the introspection and the freaky intellectual/mental activity.
There's an interesting "opposition" of some qualities: for example, sex is not importnat to Gemini suns generally whilst it has a very different relevance for Scorpio, and the elusive, low-profile personality of the Scorpio is integrated by the natural skill in interpersonal relationships of Gemini.
I won't go much into that - maybe once I am advaced in Astrology I'll do my share of research, and write a book about Mercury and another about the Gemini/Scorpio thing.
This just to say that, even though the choice of Mercury could seemto stress some parts of my character and mostly "outer" Air-related ones, it includes in a different version of itslef also the darker deeper ones, more water-like.