I voted for the Murcielago but I regret my vote. I like the Murcielago because it was the V12 Lamborghini that was around during my teenage years, the Diablo being too old for me to idolize and connected in my head to the word "Chrysler", and I even got the pleasure of seeing it being built at Sant'Agata, along with the #13 and #14 Reventons. But, having mentioned the Reventon, there's something I love about the Aventador which makes me prefer it to the Murcielago after due consideration: the one-offs Lamborghini has made based on it.
To this day, the Veneno and the Aventador J are my absolute favourite Lamborghinis, tied at the top with the 350GT. The proportions and style of the Aventador just lends itself too well to this wild, unhinged creations, I love it!