We used the following kits in our mechanical engineering program.
K’nex Solar Power-This kit is cool because it teaches solar energy. The only drawback is that there is no remote control so when you build a car, it just goes in a straight line.
K’nex STEM Explorations– This kit was pricey and the programming part was a bit anti-climactic. Problem solving skills are important when placing add ons to make your contraption do other things but the other things are not as fun as LEGO Mindstorms. This kit cost $450 yet you have to download the manual from the CD in color. WHAT?!
The great thing about K’nex is that you can use K’nex pieces to make whatever you want. Imagination is endless.
We did LEGO Mindstorms two week ago and it took them 1.5 hours to build. K’nex to 1 hour.