in terms of cost there is very little difference. Goldfish grows larger and will require a larger tank to allow them enough room to grow. You wont need an heater for your goldfish but both requires good quality filters matching the size of the tank.
both require the same level of maintenance the goldfish maybe even a bit more.
so to decide you need to think about why you want fish and what your expectations are.
Goldfish are calm slow swimmers who's attraction is their personality, they are large enough and different enough from each other in terms of colour and patterns so you can identify them as individuals. They are easy to care for if bought healthy and proper maintenance is done.
tropical fish selling point is the number of variety of shape, size , colour and behavior .
if you want lots of colour and an active tank the tropical fish it must be you can get types that wont grow over an inch if you prefer small, or larger if you prefer, you can get those that school you can mix and match many species in the same tank.
most of the popular one are very easy to care for providing you pay attention to their needs.
the most difficult part of owning a tank is the prep work before(choosing the right size tank and matching equipments) and just when you get a tank(choosing the right fish and not adding too many to start) and you have to cycle it.
if that is done well then its a 20-25% water change(for a 20 gallon tank this takes about 15min) once a week and a good cleaning every 2mths
feed sparingly and you will be happy
