I assume you are referring to this: http://mtm.cba.mit.edu/toolheads/spindle/makeit.html
As it sits with one AC (Angular Contact) bearing the MIT one is better.
Angular contact bearings are used in a minimum of pairs, sometimes triples if there is an extreme amount of force in one direction. Unlike a standard radial ball bearing where the load force is intended to be towards the side of the shaft or a thrust bearing where the load is in line with the shaft the races of an AC bearing have the ball contact at and angle, usually somewhere from 15 to 25 degrees from radial, that acts to take up thrust and radial load. To remove possible run out the bearings are preloaded so there is pressure on the balls. The amount of pressure depends on a lot of things, RPM, load, lubrication, etc. Often AC bearings will come in a matched pair that will have the inner races ground so when they are assembled and the races are locked together they will have the preload set.
I would say the rotozip is still better.