Sword leaf suckers are tapered with a large base and possess small narrow leaves. The following sucker should be one which has developed directly from the parent plant and sword suckers usually fit this criterion. Vigorous sword suckers that originate from deep-seated buds should be chosen. Vigour is essential because it indicates the place of origin. Deep-seated suckers are less prone to blowing over. They usually develop well out (about 10-15 cm) from the parent plant. Water suckers have broad leaves at an early age and also lack the distinctive taper of sword suckers. Water suckers usually develop from the corm of previously harvested plants. They are unsuitable as followers as they lack a strong attachment with the corm of the plant and thus suffer from early nutritional deficiency, causing production of small uneconomical bunches. They take longer till bunching and are also more prone to falling over. 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. Also, They are more than OK to use. Not only speaking from my actual tested experience in the tropics and here, I also came across several scientific articles in very credible scientific journals discussing the merits and advantages of using the sword-sucker types of pups over the umbrella types. This is the practice done by most banana growers when replacing plants damaged in-situ as they grow very quickly. They grow several times faster than a the same height tissue-cultured plant, and also bloom much earlier, and with tremendously bigger bunches of fruit than either the tissue cultured plantlets or umbrella types of pups. Of course in time, the tissue cultured plants or umbrella types of pups will produce sword sucker pups of their own and after the clump has matured or mat has grown wider, the differences between the two types should no longer be noticeable except that the other one gets established much faster, perhaps 6 months to 2 years ahead. When you take out sword sucker type of pup, make sure to chunk out with it, the biggest portion of mother corm that you can get away with, without dramatically damaging the mother plant (if it is still there in the clump). Other people also confused the definition between sword-sucker, umbrella, and water types of pups and wouldn't know what they are throwing away. Sources: https://www.daf.qld.gov.au/plants/fruit-and-vegetables/fruit-and-nuts/bananas/banana-sucker-management/managing-following-suckers http://forums.gardenweb.com/discussions/1734101/water-vs-sword-suckers