Aqua is the most attractive but stupidest while Darkness is just plain creepy and would probably end up suffocating you with those knockers (or end up killing you by accident), Megumin is easily the best choice not to mention the cutest of the three and it's not like you can just be friends either.
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You are now blinking and breathing manually.
http://i.imgur.com/91NC0Cb.gifv