Of course, with so many splendid games, the difference between their respective merits is often marginal. Anyway, these are the games that I always look forward to playing and/or have had their good share of table-time.
In alphabetical order:
DIE MACHER (but we play a hybrid version of the first and second editions)
LINES OF ACTION
I pondered long over NEULAND, which I consider a perfect game. However, it is now probably better known in a revised version that has destroyed its original elegant concept. So I wouldn't wish to get the two versions confused.
I also accept that LINES OF ACTION was originally a set of rules in a book to be played on a draughtboard with a standard set of draughts. However, it was later published as a stand-alone game (L.O.A) by Hexagames.