JoeReal

Most plants that produce suckers will tend to have these two kinds and some are in-between kinds though. Even asparagus, bamboos, and other rhizome producing monocots have this tendency.

Adaptation-wise, this is advantageous to the plant. The sword sucker type are best suited when there is competition around. The plant need not spend its resources on the leaves when its priority is to get as fast as possible to the sunlight, ensuring competitive edge in a denser environment. That is why this naturally happens when your banana mat is wider or the clump is denser, and that is why the sword type pups are designed to grow really fast with bigger sturdier trunks. The leaves will be formed when it gets a big headstart. Some varieties will have mostly sword sucker types though, even if the mat is not dense, perhaps these cultivars have adapted to the usually dense settings. Of course there are some advantages to the umbrella type pups in a very sparse setting. These pups are well ahead photosynthesizing very early on to help the plants gather more carbohydrates needed to form sword sucker type pups when it gets too crowded. I speculate that most dwarf types originated from umbrella type suckers when these sport mutations become etched into the plant's genes, but that is just my speculation.

I have removed sword sucker types of pups when they are just 1" tall, but that is almost a near laboratory condition. The best in my experience is to separate them when they are at least 1 to 3 ft tall at the trunk, depending on the variety, just before the leaves start to become bigger than 4" wide. This way, you don't need to trim off the leaves when transplanting them, They are the fastest growers among other types of pups as they were designed to be, from my explanation above.