i really love all Anubis varieties. It was my first love in my relationship with planted tanks years ago and will always have a special place in my heart. Now though I have begun to appreciate all the different types of crypts, the harder to find/grow types. I have quite a few rarities in the journal in my sig "crs/crypt playground.
But, for an all time single favorite plant I would have to go with Polygonum Sao Paulo. It add a beautiful red coloration to any tank and is about the best behaved stem I have ever kept. It grows pole straight up and down and can be made into a beautiful stand if you make it happy and have a little patience.