Most enthusiast will choose freshwater to start with.......Saltwater or marine fish are a much more expensive. They are also much more difficult to maintain...They are better left to someone with more experience. ..................(later, ok)

Freshwater fish live in a variety of different environments and they must be able to adapt rapidly to varying conditions. Because they are so adaptable, they can stand minor mistakes by the beginning hobbyist. Saltwater fish come from very strictly defined conditions; in the wild, it would take a major crisis to change their natural environment in a meaningful way. Though saltwater conditions are easy to duplicate with modern seawater mixes, the fish do not adapt well to changes. The aquarium must be kept in good running order, and frequent partial water changes are needed to maintain stable water conditions. In addition, the daily feeding of marine fish requires more attention. You can't simply drop some food pellets into the tank and go on a week's vacation the way you can with some freshwater fish.