I'm doing this on my phone so please disregard the typos. It'll be a little less detailed too.
As you mentioned, the sea services train together. The only difference during flight school is that the Coasties have a slightly abbreviated syllabus where they don't do forms or aero during primary, which is really too bad.
Naval Aviation has a different mindset than the Air Force both in training and operationally. During flight school you will be sort of thrown in over your head and expected to figure it out. Your time is your own and the expectation is that you will be an officer and get your studying done, unlike the Air Force where they make you sit in a room and study like 6th graders for 12 hours because you're not trusted to work hard without being forced (or something). If you're not flying, you don't have to go in to work. You are expected to manage your time, but if you do spend all your time drinking on the beach it'll be figured out and you won't pass flight school (or get what you want).
In the Navy or Marine Corps, your odds of getting helicopters are extremely high: both services have more helos than pretty much anything else (except for plopters in the Marines, but more on that in a sec). Rotary advanced is a good time and you'll get a decent feel for the different communities in the Navy and USMC.
In the Navy, your options will be (essentially) between MH-60Rs and MH-60S. There are two MH-53 squadrons that do anti-mine...stuff...in Norfolk but spots for that aren't that common and it may be gone by the time you're selecting.
Sierra pilots will tell you that they fly SEALs around and shoot hellfires all the time but that's not really true. They're a sort of workhouse for the Navy: when deployed they fly SAR missions for the carrier or the amphibs (or, fly in circles during flight ops next to the boat), do vertical replenishment, or (pretty rarely) help out with VBSS and anti-piracy stuff. They seem generally much more laid back than some other communities and are sort of jacks of all trade and masters of none.
Romeo guys ("Bromeos") are much more focused on anti-submarine stuff. Their training is much longer than Sierras (they do the entire Sierra syllabus in the FRS basically, then take care of their sub stuff). They're more likely to deploy on small boys (DDGs, etc) but also go to the carrier. They'll do some of the general helo stuff, but mostly they focus on anti-submarine warfare (ASW) and work with the P-3/8, sub guys, and SWOs to make it happen. Because they need to know "more" than Sierra guys, they're stereotypically slightly less chill than Sierra pilots, but still pretty laid back.
In both you'll spend plenty of time flying around looking at water. I liked a lot of the Navy instructors in flight school and like most of my peers that fly Navy, but they have a very different mindset than the Marines and are much more...chill about work.
The Marine helo communities are basically split between skids and 53s. I'll abbreviate this since you didn't really mention the Marine Corps (even though it's kind of my thing).
Skid squadrons (HMLAs) have both UH-1Ys ("Yankees" or "Hueys," never "venom" because that's dumb) and AH-1Ws (or AH-1Zs on the west coast and eventually everywhere). Yankees do a little bit of everything (assault support, close air support, command and control) but with a very strong emphasis on shooting. Cobras shoot and that's about it. Normally they'll fly together in a mixed section or division of 2-4 aircraft. Skid kids are, stereotypically, hyper competitive a-holes who eat their young. There's a lot of truth there, but it's more that the community takes its job very seriously and has extremely high standards.
53s in the Marine Corps do exclusively heavy lift and assault support, which since I didn't define it before, is inserting/extracting troops via the "normal way," as well as fast roping, SPIE rigging, and some other weirdness. The community is a good one: they're professional and focused on their job, but much more laid back than skids.
Ospreys (plopters, the devil's whirlybird, the fork-tailed [expletive] wagon) kind of count as helos. They do medium lift assault support and are the core unit of the air combat element in the MAGTF. Traditionally, the community they replaced (phrogs, the CH-46) was overly laid back but that may change with the switch to Ospreys.
In both services, you will fly sometimes and have a ground job always. Your ground job could be writing the flight schedule, being in charge of a shop of maintenance Marines/Sailors, or having an "S" shop (admin, logistics, comms, etc.). On showing up in the squadron you'll be put in a job with less responsibilities and as you progress and get more competent and qualified flying your responsibilities will increase.
As a pilot, you always have something to work towards. At first, it's your HAC (helicopter aircraft commander) qual. Then it's section lead, division lead, etc, etc. The rule of thumb is that of the three things you're evaluated on (officially or unofficially), your flight performance, your ground job, and how well you get along with your peers, you need to be good at two to succeed.
That ended up being way long but hopefully that helps.