Best kind of goldfish for a 30 gallon tank?

I's like a pair or trio of goldfish for my tank. It will have a good filter, which I still havent figured out yet, but it will be good. Do the bubble eye always stay on the bottom? I likw them but they all seem to nose dive to the bottom of the tank and lay there most of the time. Is there a smaller type that would allow for 3 in this size tank? I like the Shubunkins but they get too big. I'd like something relatively fast growing too. There will probably be a heater set low, if only to keep the water steady. And lots of fake plants.