All of those listed are very difficult to be in. In the Army, you need at least two years of experience to enter the special forces. If you want to see action, I recommend the Marines. With USMC, you can request to be infantry, and you will most likely get the position. With the Army, you can apply to be infantry, but you might end up as something else, at least if you are an officer.
USMC practically guarantees you the position you want, and joining Force Recon is easier than joining the Rangers.
But, since we are sending 30,000 more troops into Afghanistan, it is highly likely you will be deployed no matter which branch you choose.
