The kebons are good, basic forms, and are common to both karate systems and taekwondo systems. Though there are three to five of these, I don’t usually count them as forms because they are learning the important but easy ABCs of the martial arts.
The next batch of kata to consider would be the Taeguks from Tae kwon do. These are basic moves, a bit more advanced than the kebons, but not as advanced as the Okinawan Pinans (Japanese Heians). Though they take a few moves from the Pinan forms, they serve them up as straight block and counter techniques, no hidden throws or weapons disarms, and no real generation of internal energy.
After the taeguk patterns one should move directly into the Pinan forms from the Shotokan system, the shito ryu system, and other Japanese martial styles. The Pinan kata are actually designed more for weapons defenses and disarms, though not many people know that. The idea here is that one studies the Taeguk patterns for hand to hand combat, then moves into the Pinans for a basic understanding of weapons disarms, and the beginnings of chi building.
After the Pinans I recommend the three forms from Pan Gai Noon, which is the base art of Uechi ryu Karate, and which are actually three extremely hard core kung fu forms. These three forms are sanchin, seisan, and sanseirui, though sanseirui is considered more of a show form. These three unique kata are specifically designed to generate internal energy.
The Sanchin form teaches a student to fasten the body/motor to the ground. There are not a lot of moves in it, but the moves are excellent for teaching one to use hard energy in self defense moves.
Sanchin may be the form that builds power, but seisan is the kata which builds technique. This form takes the power of sanchin and creates (probably) 13 specific self defense moves. These are all based on one specific motion called wa uke, which is a circle block with a grab on the end.
So, taekwondo to karate to kung fu; Kebons to Taeguk to Pinans to Sanchin and seisan. This arrangement of martial arts forms provides the student with the absolute best and most complete sequence of classical training there is. Other forms can and should be studied, but this is the heart of the art right here.