If your foundation is cracking, it is because the soil beneath the foundation has not been capable of bearing the weight of the structure. This can be caused by a foundation which is exposed to rainwater from gutters which do not direct the water away from the house, and I see this a lot in home inspections.
As far as fixes are concerned, go with the polyurethane, as it should be more flexible as the concrete expands and contracts, and possibly cracks more as time progresses. (the repair may be twice as expensive now, but if you have to redo it in a couple of years...)
Make sure you understand why the foundation cracked in the first place. This is very important, especially if the fix is as easy as buying some splash blocks for your gutters and making sure the water doesn't pool against your foundation.