Nukes work, can pre-empt or meet a launched missile.
Airborne laser (Boeing ABL) cannot take out anything ie will never work.
See e.g.
http://optics.org/articles/ole/7/5/5/comment/view/53 and also note (quick search google?) that the engineers are not able to get 6 laser chemical (COIL) modules on board, they need 14. These are individual lasers, next to impossible to make one coherent beam. Jitter requirements are such that the laser can not meet them on a plane. ABL is mega heavy, beam breaks up at much shorter range than desired, and the plane is shaking like mad from a lasers point of view.
ABL is a cash cow. That's all.
Army's THEL (tactical high energy laser, do search?) works, has taken out multiple katuysha's and artillary, some missiles albeit at close range. THEL works, worked quickly.
ABL cash cow has been going on for over ten years under this name. Will never do a test (moved from 1999, 2001,2002, 2003, 2004, to 2005!), will never work, and "Jerry's kids" (MDA) has staked its hopes on ABL, although backing off somewhat lately.