Do a search - there has been a lot of information about this in different boards.

Just my opinion:

LH and SQ are lightyears over Asiana in C and also in F.
The Asiana C seats are not even comparable to the old C seats on LH and SQ. Friendly service on Asiana but that is about it. Very dated planes, very uncomfortable F seats also. I try to avoid Asiana whenever possible.

SQ and LH in F: no clear preference for one of the two. The LH seats on the 747 are better when travelling with somebody, the seperate seats on SQ are nicer when travelling alone. I sleep in both well. Slight preference o SQ, because F in the nose is more quiet. On the Airbus LH has single seats, which i prefer over the coffins on SQ.

LH food is more european, SQ asian - so whatever you like more. SQ service is more polised, perfect, but sometimes not personal. LH is sometimes borderline rude, but good most of the time.