That's a tough one. AF has way fewer helo's, but it's harder to get a slot there than in the Navy/USMC. Navy/USMC is over 50% helo pilots - not that's a bad thing
(I flew H-60's for 5 years and then got to switch to E-2's; the H-60 was WAY more fun)
USMC will guarantee you a pilot slot early in the process, but you will still drop 9 months at "The Basic School" learning how to lead Marines in the field. They want Marines first, aviators second so if you're not into digiflage (new cammo) don't go. Navy doesn't have that requirement, but you won't know if you got a pilot slot until past the "commitment" line. You could end up on a ship (insert hanging gesture here).
That said, even if you get helo's, you'll fly a T-34 first (about 120 hrs), and can go back as an IP after your sea tour or go fly C-12's (King Airs) and get your airline prep time that way. I've never heard of anyone having a problem getting hired after instructing or going C-12's. IP'ing is more turbine PIC, but you're on your own for ME/ATP. In the C-12 you'll get less PIC, but it's MEL and they usually have a deal set up to get your ATP on your annual check ride.
Others here can speak better of the AF.
HTH
Spongebob