Of course, for a first time visitor, or even more experienced visitors, the choice of a way to get "home" (to a hotel) is binary. For example, it's either cab or a train.
But, once you understand the totality of all features of all transportation options, including the problems you may face, you might start mixing and matching.
For example, the only available flight to get me home after a business trip took me to JFK. But it was still rush hour. And I despised the Van Wyck. And the Belt Parkway in Brooklyn was only slightly better. And there was no way I wanted to be bumper to bumper in a standstill trying to get into Manhattan. Solution: take a cab along the Belt Parkway to nearby southern Brooklyn (Sheepshead Bay) where I could get to the corner of Avenue U and East 19th Street to go to my favorite Vietnamese restaurant, Pho Hoai (far better than anything in Manhattan; Flushing, Queens; or other areas of Brooklyn).
I'd eat there, stroll to the Q train Avenue U subway stop, take the express train when I could get it, and get into Manhattan in no time. And that wasn't a way to save money, as I would get the cab ride reimbursed by my company anyway. It was a way to (1) bypass the traffic nightmare and (2) eat where I loved to eat.
Once the OP gets his subway map, he'll see what I did.
The only reason I make mention of that is because there are more simple mixing and matching that even an adventurous newbie might try, especially during rush hours. Get a cab out of LaGuardia to take you to the nearby subway station. And then subway to the Marriott Vacation Club.
The cab driver might hate you as he may have had to wait some amount of time for that few minute cab ride....but that's his job. And you can give him a good tip. And he can get back in the queue in no time. And, hopefully, get a longer ride next time. It all balances out over time. Plus, even he may not want to sit in a parking lot on the way to Manhattan.