Which tank is the right tank

I have a freshwater tank for a year and 1/2 and i want to start a saltwater tank. i have a 15 gallon column tank a 20 gallon tank and a ten gallon tank. i was wondering which one would be better for a nano reef. also i want to have a pair of clown fish, anomen, some coral, and some inverts. if you have any suggestions on which of these things would be good also some of the powerhead how much light and if i need a special filter. i understand it will tank a long time to cycle so i want to start it soon so it can be done sooner so any suggestions would be really helpful.