The Chon-Ji patterns were created by Choi Hong Hi, founder of the ITF. There are 24* patterns used -- 24 being the number of hours in a day, thus a metaphor for a man's whole life. The first nine patterns in this series (those meant for gup ranks) are probably the most difficult of the hyung compared to those in other series. This is the only pattern set that requires a student to perform jumping and flying maneuvers on their way to 1st dan. The footwork involved in these patterns in also the most complicated. The typical school requires a student to master the first nine patterns (Chon-Ji through Choong-Moo) for advancement to black belt. The patterns are named after significant people and events in Korean history.
The black belt patterns are also very complicated and present new and unique challenges as one moves through the ranks. Many of the patterns are very long, containing more than sixty techniques each. Some patterns require additional physical training to learn and master one or more newly introduced moves. All in all, the black belt patterns in this set are very demanding.
* There are 25 patterns listed on my site. The pattern Ju-Che replaces Ko-Dang in the modern ITF curriculum. However, the USTF allows students 35 and over to substitute Ko-Dang for Ju-Che during testing. (Ju-Che is probably the most difficult and physically demanding pattern listed on this site.) Some masters only teach 20 of the Chon-Ji patterns. In addition to Ju-Che, four more (of the 24) were created later than the "original" twenty. The "newer" patterns are Eui-Am, Moon-Moo, So-San and Yon-Gae.
The Palgue patterns were the "original" WTF patterns for gup grades. They fell out of favor in the 1970's because of the Japanese influences in the patterns' techniques. They were replaced by the Taegeuk pattern set. Traditionally, the WTF student learns patterns 1 through 8 and the black belt pattern Koryo on their way to 1st dan. These patterns are regaining popularity, though, because of the over saturation of the Taegeuk in tournament competition.
The Palgue set is certainly more difficult than the Taegeuk patterns that replaced them. While patterns 1 through 4 are relatively easy, patterns 5 through 8 each present their own unique challenges as more difficult techniques are introduced.
The Palgue patterns are an excellent hybrid of modern Taekwondo techniques (e.g. those found in the Taegeuk set) as well as introducing several complexities that are more common in Japanese patterns (like the Shotokan patterns described below.
Heian (Pyong-Ahn) Patterns
These patterns originally come from Shotokan karate where they called "Heian". They were imported into Taekwondo sometime during Japan's occupation of the Korean peninsula (1905 to 1945). Many traditional schools still teach these patterns under their Korean name, "Pyong Ahn". The set is composed of five patterns, increasing in difficulty. These patterns are relatively short -- each of them have fewer than 30 techniques. They are usually used as introductory patterns in Taekwondo schools as well as Shotokan dojos. In Shotokan, students must learn these five patterns and the three Tekki patterns on their way to black belt.
Shotokan Black Belt Patterns
The Shotokan patterns for black belts present the greatest challenges for the Taekwondo student. Shotokan karate uses many techniques that are uncommon in Korean martial arts. Fortunately, Shotokan is a very scientific art, meaning that most superfluous stances and techniques have been refined and eliminated. Therefore the Taekwondo student will have only a moderate amount of difficulty learning these patterns. Of course, it should go without saying that these are black belt patterns. Consequently, they are all relatively intricate and present several new techniques for the black belt. Because of Shotokan's enormous influence on Taekwondo during the Japanese occupation of Korea, these patterns provide a jumping off point for the advanced student to explore a similar style's hyung.
Many traditional Taekwondo schools still teach some of these patterns. The most common of which are Bassai and Kanku. Their Korean names are "Bal-Sek" and "Kong San Koon", respectively. Schools that teach other black belt patterns usually retain the Japanese pronunciation or sound very similar.
The Taegeuk patterns are the most recently developed patterns for the WTF student. Typically, a student learns patterns 1 through 8 and the black belt pattern Koryo on their way to 1st dan. They were developed to replace the older Palgue pattern set which fell out of favor because of the Japanese influences in that set.
The Taegeuk patterns are probably the easiest to learn when compared to the other patterns for gup grades (color belts). There are very few complex techniques and none of the movements are physically demanding. If you have studied any other pattern sets, then making the transition to studying the Taegeuk will be relatively easy.
The primary benefit of learning the Taegeuk set is its popularity. Because they are the "official" pattern set for the WTF, they are widely accepted and well known at tournaments.
WTF Black Belt Patterns
The WTF patterns for black belts vary greatly from both the Palgue and the Taegeuk. Not only are they far more difficult to master, but they are more complex and of a different style than the patterns studied during the gup ranks. Like the ITF black belt patterns, these forms introduce techniques that require additional physical training, as many movements are not often practiced or used prior to learning them in the pattern.
Each pattern is slightly different in style than the others, but not in such a way that they lose their continuity. This makes learning the WTF patterns a bit of a joy because each one is independent of the other and each feels completely 'new' when you first study it.
Tekki 1 - 3: These are unique patterns in that they are all done in a straight line and every stance is a horse riding stance. In this regard they are similar to Po-Eun of the Chon-Ji patterns and Pyeong-won of the WTF patterns. In Shotokan schools these patterns are required (along with Heian 1 through 5) for advancement to black belt. Taekwondo schools usually only teach the first of the Tekki which they call "Chul-Gi".