Marble Runs combine many of the skills and creativity of construction sets with kinetic play that demonstrates physics in action. Hape and Mindware make excellent sets, the former mostly of wood, the latter of multi-colored plastic parts.
Keep in mind that both companies have many sets, priced generally according to how many pieces are in the box. For instance, the Q-Ba-Maze 2.0 Colossal Set has 186 cubes plus eight that light up, 40 steel marbles, tubes, stunt pieces, and more; but, it carries a $199.95 price tag! You can also find Mindware starter sets for as little as $50. So, unless your child is already dedicated to marble runs, it might be better to start with one of the medium sized kits, one that has enough pieces to challenge but not so many as to break the bank, and see if it is a hit before investing in a mammoth collection.
Three sets I like with very different price points are:
Hape Super Spiral Quadrilla ($164.99) is a massive set with multiple spirals, a xylophone, see-saws, and other specialty bricks that make designing runs creative and fascinating to watch. An app helps teach how to build runs and how to make the most of the over 120 pieces that come with the set.
Q-BA-Maze 2.0 Lights ($59.95) dispenses with the wooden bricks of the Hape sets in favor of multi-color plastic blocks, tubes, and stunt pieces that can stack together in even more far-out designs. The Lights set even have pieces that illuminate for fun-in-the-dark ball runs.
Blue Orange Tumble Maze ($24.99) is a gravity driven puzzle game. You have to solve increasingly difficult puzzles by placing ramps as needed to get the three steel balls from Point A to Point B. If the Hape and Mindware mazes are three dimensional, these puzzles are more 2D. That doesn't mean they don't take serious effort to solve, with the added bonus of taking less time to put away!