Setting up a goldfish community tank is often a tricky process and basically what you need to do is to group together all the fish that has the same attributes and characteristics so that they can co-exist with each other without anyone getting left out. Here, I’ll try to separate them apart so that you can easily follow and make your choices.
Fast swimming goldfish
All the varieties in this group generally have good eyesight and they will not have any restrictions to their ability to swim normally. Thus, they can easily compete for food and will be the first to grab whatever you put into the aquarium before other does. Fish categorized in this group are like black moor, shubunkin and also common goldfish like comet and wakin.
The average swimmers are those that have fair ability to compete for food and will have slight disadvantages compared to the fast swimming group. Among the fish that belongs here are like veiltail (with their long trailing tail that slows down movement in the water), oranda (with raspberry growth on the head that covers their eye reducing visibility) and ryukin (with the wide and high body).
Fancy Goldfish/Extremely slow swimmers
Goldfish in this group will always find it difficult to compete for food if mixed with other goldfish varieties because of their handicapped nature. For example, bubble-eye has a sagging pouch beneath their eyes and this will slow them down considerably. Tosakin also is another handicapped type because of their horizontal flat open tail fin which will make them hard to push across water. Other goldfish, which also belongs here, are ranchu with their round and stout body and the slowest of all is pearlscale with their short fins and ping-pong shaped body.
In order to choose the right type of different goldfish to mix into your community tank, basically a good combination is to have all the fast swimmers into one aquarium and all the average swimmers into another one while the fancy goldfish should be separated from the rest. If you have intention to mix among different groups, then my advice is to choose one or two among the fast swimmers and then mix with the lot of average swimmers, which could still be ok, although this is not a recommended thing to do. Other things to take note is that, make sure you get the right tank size for your goldfish so that they don't get stunted because of space limitation.