Any of the following species all are candidates for fast growth, based on how many of it's needs are met and not limited in any way:
Ludwigia. Just about any of the species are fast growers.
Hygrophila. Wisteria is nice and fast.
Rotala. Rotundifolia is nice. Most are ez except maybe macandra...
Amazon swords - many of these grow quickly whether large or small. Many produce numerous leaves very quickly.
Remember that any plant will grow better with more c02 and nutrients, lighting, etc.
Many plants will grow more quickly with these things in adequate supply.
Plants which grow slowly when down near the substrate, can become racehorses once they get tall enough to get the more intense light they want. H. difformis is a good example of that, and for me, once it starts growing fast anywhere in the tank, all parts at any level in the tank seem to join in the race. L. aromatica is another that I found to grow increasingly fast as they get taller.