If you want to fly helicopters, the
Marines is the only branch that offers guaranteed pilot slots for officers.
But it is very competitive and entails an 8 year active duty commitment.
The Marines are the smallest of the four services with the smallest budget. You'll be flying older model helicopters on average. The Marines also has a unique culture that isn't for everyone. They expect everyone to be an infantryman first, so you will be spending time rotating through non-flying positions throughout your career.
The Army has by far the most helicopter pilots, since it has the majority of the US military's rotary wing aviation. There are two different ways to become an Army helicopter pilot:
officer or
warrant officer.
Aviation Officer:
There are no guaranteed Army Aviation officer slots. The best way to get a slot is to:
a) do ROTC while in college and graduate at the top of your program
-AND-
b) agree to incur an additional active duty service obligation (ADSO) in order to be assigned the branch of your choice (Aviation). I'm not sure if Aviation branch requires an aviation degree to do this.
-AND-
c) hope and pray the Army needs a lot of helicopter pilots that year
Bottom line: If you can get a pilot slot, you are looking at 7-8 years of active duty. And there is no guarantee the Army will assign you as a pilot. Once you sign on the dotted line, you are subject to the "needs of the army." You may well end up as an infantry officer or chemical officer. You can always compete to transfer into Aviation at a later date (it's called Voluntary Transfer Incentive Program), but again, such transfers are subject to needs of the army.
:
The second route is to become a Warrant Officer. There's a program called "high school to flight school" where you can enlist with a WOCS and flight school contract, meaning you are guaranteed slots to Warrant Officer Candidate School and Flight School.
Unlike Army or Marine Corps officers that fly less and less as their career progresses (they must perform management and admin jobs that take them out of the cockpit), flight warrants have one basic job: fly. Again you are looking at ~7 year active duty commitment if you become a flight warrant.
You can also become a flight warrant by first enlisting in the Army, then before your enlistment is up, apply for WOCS. In this case, you'll be spending a couple years as a grunt. Since pilot is the goal, it makes sense to enlist in an aviation-related field, such as helicopter repairer.
I don't mean to scare you or dissuade you. Just letting you know what you are in for if you decide to go that route.
Even if you don't want to be a pilot, there are a lot of great opportunities in other fields. Plenty of Logisticians end up making six figure salaries after they get out of the military doing things like supply chain management for Amazon and UPS.
If you stay in past initial entry, there's a plethora of opportunities, including special operations fields. One of the best kept secrets in the military is Army Foreign Service Officer. The government actually pays you to learn how to host cocktail parties for foreign dignitaries and be an international arms dealer (that's not a joke,
the US sold $55.6 billion of foreign military sales in 2018).
