I feel I may be in the minority on this one - I've had fresh and salt and salt is the way for me. While we can't duplicate
the ocean, there's no question in my mind over whether many creatures living in the ocean can live and thrive in closed environments. Careful selection and maintenance are unfortunately not a given, which may be a turn off for some people looking in in the hobby, but every individual who takes the time to learn their stuff can help improve the industry and reputation!
I agree with Autumn and Bribo, everyone will have a different personal opinion and choice on aquariums. Lifestyle, commitments, money, personal appeal, and location all factor in.
Costs are different, but it's important to see the range in both sides. You can build a 3g reef for $250 or a 10g fw
for the same. The price will be the same but everyone will choose differently.