It really could depend on your taste... I have only gone with freshwater because of the costs and the work in them. Overall Saltwater is going to offer a lot more color and activity... Personally I could sit and stare at a tank that had nothing but live rock in it... you often find lots of little creatures... they are exciting. But if you try hard enough you could put together a real nice freshwater display that would make you quite happy. There are many, many fresh water fish to chose from... and in a 55 gal
you should be able to make things interesting... some live plants, some neat hiding places... you could have several types of bottom feeders... khuli loaches(attractive), corys(active), violet gobys(aka dragon fish) are pretty cool... then some fish that swim higher and at different ranges in the tank.. there are pleanty of fw
fish that have color to them. You'd have to decide if you want an aggressive tank or a nice friendly community tank. Like I said I chose fw
because of the low costs and low maintenance but if you have time and money salt does have more to offer... I was at petco the other day (not to change the subject) and saw these little fake octopi that supposedly would swim around in your tank as long as there was some current in it. I didn't buy them but they would be interesting to see.... Anyway... whichever you chose you should be able to set it up to be quite pleasing... good luck...