What metro/subway do I take from La Guardia to Penn Station? Thx

Take the Q70-SBS bus to Roosevelt Ave/74 Street in Wooside switch there to the E train heading to Manhattan and get off at Penn station/ 34th Street. Depending on the time of the day it should take about 45 minutes.

I used google maps and was quite satisfied with the results.

When I was in NY I used the app Citymapper and it helped give me options on different travel routes. I know there are other ny transportation apps too to help out, though honestly the yellow cabs are great to and from the airport and they have a new app Curb now