The largest are, of course, the commons/comets. Of the fancies, Orandas tend to be the gentle giants of the water, but just about any other breed can get as large. The "length" of a fish can be misleading, for the size of a fat Ranchu at only 6-7 inches is HUGE - they are MASSIVE fish, where a looooooong, streamlined comet is much larger in length - it has only about the same mass at 10-12 inches.
Pearlscales tend to be a bit smaller - but they can make up the difference in mass - sometimes being fatter than they are long. Bubbleeye fish are about the same general size as the Pearlscales - I have seen them at 6-8 inches but not much more. Ryukins are as deep as they are long - and thusly can be massive.
Pearlscales, Bubbleeyed fish, Celestials, Fantails, Telescope eyed fish, Ryukin/Lionhead/Ranchu, ORanda, Shubies, Comets, Commons are a VERY rough guess as to size from smallest to largest.
Each fish's final size is greatly affected by several factors. One of the most influential is genetics. Within a single spawning of fish, you will have ones that easily outgrow their siblings - and ones that never seem to quite catch up. The big ones are perhaps the ones destined to be the monsters of the tank - the others, still great fish, are nice, average beauties.
The next most influential thing is culture - how the fish were raised from the day the eggs were laid. Plenty of good quality water and proper temperatures, along with the right amount/type of food go a long way to give the fish that carry the genetic potential for great growth a chance to fullfill that promise. A fish that was crowded in poor water with a lack of quality food will not grow as well as one that was pampered.
Time is the final thing - most fish do the majority of their growth in the first year of life. They go from a tiny thread size to a massive fish in a very short time. If the environment does not support this growth when they are young, they lose out on much of their best growth time in life - and will not be as big as those who have it all. All fish will continue to grow throughout life - but they slow down as the years pass. The presence of disease/parasites can dramatically slow a fish's development. They may not be problems serious enough to kill the fish, but they do not thrive as they would without such problems - and growth is slowed.
Because of the potential size of all these fish, it is essential that keepers realize what they are getting when they purchase that red flash of scales that catches the eye in the store tank. That fish can be with you for several decades - and grow to need at least 20 gallons of water - for some 20 is way too little.