IIRC you are limited to the LH business class lounges (unless you have *G status in which case the LH Senator lounges are also available).
I'd generally go for the lounge closest to departure gate, but since you have time you could sample them. Assuming you are arriving from USA then you have non-schengen to non-schengen transfer, which means if you leave the airport or visit certain parts of the terminal you'll have immigration twice (once to enter schengen zone and again to leave it). You are also likely to have at least 1 security check in transit.