what is the best kind of cement for filling cracks in foundations?
I would not suggest cement. There are epoxy systems for strucural repairs or several types of products for water infiltration. Using cement will cause a mess and won't do either of the above with small cracks.
Filling cracks with cement is futile. If you are filling a form tie hole then hydraulic cement is the choice. For cracks, use an epoxy filler.
If they are small cracks, you might consider Mortar Mix instead of concrete.
