I love my marine tank. There is so much I can do in it that I can't in a FW tank.
That said...I also love my FW tanks and there are things I can do in there I can't in a marine tank.
This is why I have both and as long as I'm able will. I love plants and the types of fish I can put in my FW tank and I love corals, anemone crabs, hermits, wonderful relationships like my anemone and the clowns, my tangs, my tiny coral dwelling fish like my panda clown and yellow clown goby and so much more.
For me it's not one or the other. Since I was 5 years old it's been WATER and the THINGS THAT LIVE IN WATER. From the first tadpoles I raised to frogs to the corals I keep today it's just that aquatic life is so fascinating to me that I can't leave it alone.
But...if one is just looking at the amount of effort, time, and expense...then stick with FW beccause marine can be WAY up there. My wave maker cost nearly $600 USD, the skimmer was around $300 and let's not even talk about the lights! Then there are the animals...corals can be costly...my purple tang was $180 and that's considered a good price. Cheap fish like clownfish are $19. Even my tiny little goby are $14 or more.
I set up my entire 10 gallon planted tank for around $100 and that includes everything...Co2 unit, LED to grow plants, heater, small canister, substrate, plants, shrimp and fish. And I have microfish which actually tend to run a little more so even with those it's WAY cheaper.
Oh...and just to be totally silly and picky...marine tanks are tropical too.