Like most things, this is a matter of personal preference.
Foster City is older and offers more amenities likes parks, schools, and shopping.
Redwood Shores is newer and is actually a part of Redwood City.
So if your preference is newer construction Redwood Shores is the better bet.
If you want a more mature city with a greater sense of community, I would suggest Foster City.
To check schools, try http://www.greatschools.net.
Hope this helps.