Jessica Rabbit. She's not bad, she's just drawn that way
(and really is the ultimate satire for stuff like this)
I'm actually taken aback by some of the insults I'm seeing in this thread. I'm seeing a lot of "Um...they aren't real, so that makes you a loser."
Let me ask you something. Who is your favorite video game character? Are they cool? Are they funny? Are they interesting? Well guess what...they aren't real. So clearly you must be a loser, right?
Don't get me wrong, the term waifu makes me want to punch babies and people will always associate it with the "watashi wa boku desu desu ne" pocky snarfing crowd, but it's simply looking at a fictional character and saying "Ah, they're sort of attractive and I like their personality. If they WERE a real person, I'd like to go out with them"
It doesn't mean you have a stained love pillow of them >_>
For me though in 100% seriousness, it was Princess Peach. She was my first fictional crush and she actually became a metaphor for true love in my own life. I always imagined that every failed experience I had was the life equivalent of "Your Princess is in another castle" in the sense that it was something I needed to do, it was worth doing, and it put me one step closer to finding my true love.
I had a girlfriend that I nicknamed Peach for this very reason (and a secondary reason I won't mention here...) and yes, she knew why. She thought it was very sweet and loved the nickname.