Imo I'd say FIRE!!
Sure you might be Gemini, and since Mercury is traditional ruler of Gemini, It's well placed! yet taking a close look at your sun/moon midpoint, your SN is conj within 1 degree, so you could be comfortably cancer! Having Pisces rule your 3rd house (where gemini naturally lives) there's some water affinity to this chart (well, more MOON affinity really), and with quite a strong connection to the Mutable energies (a strong Mercury that traditionally rules Virgo and Gemini, with Pisces in 3rd, and Merc/sun in Gemini, Sag AC) With that said, I want to look at your moon placement, and AC, with the AC being in fire, and it's ruler Jupiter in fixed energy, conj your moon being in Leo, Moon rules 4th house and that house is in Aries (fire) which mars, just so happens to be conj your moon, and even judging from the profile picture, My money is on the fixed energy of LEO (FIRE!!)
Saturn placed in it's traditionally ruled sign (Aquarius) and Sun in Gemini gives you a close 2nd for Air affinity.
Lets look where your chart ruler is at (Jupiter) and we find it...well wouldn't you know, Leo ^_^
Those are some really impressive squares and oppositions btw, that 8th house isn't very happy with you at all, lots of work to be done. With Saturn in air opposing your chart ruler Jupiter, and your sun/merc opposing your AC, you will see-saw between feeling like fire and air often, no wonder you asked this question!
If anyone says Earth or Water however, they should be smacked.