I chose the EOS since it's the only one that was originally built as a convertible. The 307 and the Megane CC are chopped down versions of sedan/hatchback cars.

I also love the innovative roof of the EOS. You can either tilt the sunroof, slide it, or fully open the whole roof.

Also the EOS comes with much more equipment than either the Megane or the 307.

Regarding comparing the 318 with the EOS. If I were in your shoes I would definitely buy the EOS. Why would I buy the most basic BMW while, for the same price, I can get a convertible fully loaded with gadgets and convenience features. Also the feeling of driving with the roof down is astonishing!

You guys should have a look at the 308 CC. It's utterly, stunningly, jaw-droppingly beautiful!