Khan and by a wide margin. Absolutely no one knows who Crawford is outside of the hardcore fans. To be fair though, khan isn't that known in the states either, but if they were able to fight in Dubai, I'm sure it would be very successful financially speaking.
Will be worth re-checking this thread periodically to see just how many people falsely claim Khan has a PPV-buying fan-base in; Britain, Asia and/or the US One of the biggest lies continually perpetuated regarding Khan. It would do similar numbers, but the fight would do more for Crawford long-term than it would for Khan and that's why I expect it to be Crawford. Arum is looking for his next PPV fighter.
He isn't even popular enough in the UK that the fight would be PPV either. The person who is selling either of these fights if Pacquaio. They will do very similar numbers, but Khan's purse demands will probably be 10 times higher than Crawford's. Couple this with the fact that Crawford is Top Rank...