I'm not going to lie, this wasn't even difficult for me. I would unequivocably and without hesitation save my best friend. The reason why is simple:

I am selfish and the value I would put on my best friend's life compared to those of strangers is immeasurable. You could stack the numbers of strangers as high as you like but my best friend, would outweigh them all.

Now if the situation of this thread were to be a reality and the life of my best friend cost approximately 3000 people (considering a couple of thousand is 2000 (approx) and the plane would for dramatic purposes be a 747 or bigger which means 4 - 700 people depending on the configuration of the plane then I have to say it would be a bargain in my opinion. I would feel some sadness for those people in the plane or town but frankly as they do not hold a personal connection to me I would still have been more sad at the loss of my best friend than all of them. After all, horrible as it is, this is exactly what Stalin meant by the phrase "The death of 1 is a tragedy, the death of a Million merely a statistic."