Questions about La Guardia and transportation?

What kind of transportation is safer and cheaper from La Guardia to Manhattan. We have 3 children 12, 10 and an infant. We will be staying for 4 nights so we'll have to go back and forth at least 2 times a day. Would it just be cheaper to stay in Manhattan? Or somewhere else? We dont have our airfare yet, so we can change airports as well. We will be spending every day in Manhattan.