Bandu is the simplest, made from natural wood, and ideal for beginners. Even this basic version is much more challenging and interesting compared to Jenga (which I still like). It's very affordable. Recommended.
Bausack Towers is a larger, more complex set with more interesting shapes -- but still smaller than Sac Noir. What makes this game worth pursuing is the fact that its pieces are painted red and white. One is much slicker, with almost no friction, making it very challenging to stack. It's more expensive, but absolutely worth it, and a better choice for experienced gamers or people with high dexterity. Highly recommended.
Sac Noir includes many shapes that didn't make it into the other sets -- and which make some of the incomprehensible pieces make sense. There are many pieces which are hollow, partly hollow, or have tiny drilled holes in the center. This is so you can stack them with the many other pieces that come to a point. There are also lots of matching sets between convex and concave curves. So it's potentially easier to stack things securely. I say "potentially" because what it will really do is tempt me to do batshit combinations. This is a good thing because it levels the playing field. Without the unique features of the more advanced sets, few people will want to play me because my structure sense means I always win. Not so fun. But if I'm trying to do crazy things with the blocks, it means I fail at approximately the same rate as average players. \o/ Note there is no definitive set on this edition, as the blocks were packed more-or-less randomly. This is another great pick for experts and collectors, but it's out of print and therefore expensive. Highly recommended.
Dexterity games are great for nonreaders, foreign-language speakers, and people with high visual-spatial or kinesthetic intelligences. You always want to have some in your collection if you host diverse gamers. Stacking-block games are a great way to teach young children how to play games, take turns, and collaborate. They offer real choices, unlike preset games such as Candyland.
Another fun aspect is the conversation. What do you call the funny-shaped pieces? You can get a fantastic linguistic workout this way, making them an exceptional toolkit for language learners. If I were taking such a thing into a foreign language class, though, I'd probably paint them more colors. It wouldn't hurt Bandu, and then you could use color vocabulary too.
If you have players with superpowers, you are going to need the more advanced sets, though. Bausack Towers and Sac Noir offer different advantages. Bausack Towers is more physically challenging due to the slippery blocks, while Sac Noir adds a more cerebral aspect because there are so many more shapes "made for" each other. Sac Noir has a clear advantage if you favor any of the games with a strong strategic element. (Instructions for several different games come with the set.) It is easy to come up with new games, for example, trying to make sets of blocks with the same features (blocks with four sides, blocks with a hole, etc.) in them.
Also worth mentioning: because Bandu has natural blocks while Sac Noir has red and black blocks, these two games can be combined for playing in large groups, and then easily separated afterwards. Other combinations would better be made permanent, or else dot-mark the sets differently so they can be separated after play.