I think it's a matter of contact and who you are personally that makes the difference in which one you choose.
If I've met a girl and we've been talking for sometime and she seems interested in me then getting her number would be the optimum choice. She knows who I am, she willingly gave me her number so in that transaction, which probably took me at least 10 minutes but could be an hour for all I know, this is the natural and best conclusion I could come to.
Conversely, I'm reminded of a sketch done by Martin Lawrence about meeting a girl in a group of hot girls in a night club. He presented himself in a smooth and suave manner, politely introduced himself to the girl he was interested in, pardoning his interuption. Complemented her on her apearance in a good way and gave her his card which had his number on it. Closed and exited back to his buisness. Total time taken was less then 1 minute. From that prospective you could potentially meet a larger number of girls and meet with similar results if you so desired. It's the same principle I use as a promoter giving out free passes and building my guest list daily. I know not ALL of them are going to return my efforts but since I hit up so many I know at least a few are going to take the bait. If I had done things the other way I'd be looking at a short list and probobly make no money.
I say to each his own. It's a different approach but it's like choosing between a sniper rifle and a shotgun. They'll both do the job but in different ways.
