Tailoring messages to each girl's profile is the way to go. However, if you're doing mass messaging like I do then you simply can't take the time do break down each girl's profile unless you want to make an afternoon out of it.
The line I've been using to message chicks is:
"Hey I checked out your profile and you seem cool. What are you up to?"
By saying I checked out their profile it implies that I did actually check them out which I didn't, I just look at their pictures. I messaged this to a girl one time and she responded with "I don't have much on my profile, but thanks...blah blah blah". She had like 5-6 lines total on OKC but it doesn't matter.
Edit: Here it is:
Now, when a girl visits your profile before you check theirs out I always send:
"Hey! You checked me out and didn't say hi"
It has a very high return response rate. D&P writes about it here:
http://dangerandplay.com/2011/11/16/how-...d-looking/
As for the first girl, the convo ended prematurely, but I have a date Friday with the second girl. I'm not going to say these lines always work, but I don't think any line does. Girl's who visit your profile are much more inclined to want to meet, because they clicked on you for a reason (i.e. You're attractive, in their age range, and live near them). Which brings me to my last point.
As others have mentioned, it really comes down to looks. That's why I stay away from the cute, silly openers. It feels incongruent to me. No girl is going to want to go out with some weird looking guy just because he has a witty opener. The reason I advocate my original line is that it is more complex than just simply saying "Hey" or "What's up", but it's not too outrageous that it will turn a girl off.