thepointsguy dot com has lots of great info on maximizing credit cards for travel purposes. A lot depends on your location and spending habits. Their search engine will tell you which airlines are currently Star Alliance members and also partners with Lufthansa. Pizzagirl, busdriver11 and GMTplus7 might have better input than I do…
United is in Star Alliance, and the United Explorer card will help you get those miles to use on Lufthansa. In addition, there are car insurance benefits, free luggage, and early boarding for card members. The website mentioned above has the info. You need to try to maximize your free miles on sign up, add a family member. Read the fine print before signing up.
In addition, TPG is a proponent of a few other cards that give miles to transfer to other airlines.