I wouldn’t say any one filter.
http://www.l33tmeatwad.com/scripts/anime-upscale
Ive only used it on anime that was already DVD quality but just wanted it to look better on a bigger screen. My general experience is that it will make it look as good as a DVD will on a crt except on a much larger hdtv screen. (Meaning no extra detail or anything magic like that but also no jaggies, no pixelation, little rainbow and no blocky lines or edges like you would get if you just played the DVD on a large hdtv screen)