I have a strong feeling that its peyton coz...
1) The woman who plays Lindsey (i forgot her name) got another job on another tv show (SVU i think) so she wont be around much for oth =))
2) Brooke wouldnt do that to peyton and Lucas knows that. Lucas and Brooke are great friends and Lucas knows that.
I think that it's probably Peyton.
I saw some spoiler pictures on youtube that shows Lucas kissing Peyton at the airport.