Either of the Elite versions. These are the only decent versions of this movie out there. Accept no substitutes.
I think the "Millennium Edition" might have a slightly superior transfer and a few more special features, but I'm quite satisfied with my Elite "Special Collector's Edition." Both have the Romero and cast commentaries.
Avoid the Anchor Bay 30th Anniversary edition.
Fox also put out a colorized version (which also included the black and white) -- I haven't seen it yet.
Anything else is likely to be a public domain print with a shitty transfer.
"There are 100,000 total marijuana smokers in the US, and most are Negroes, Hispanics, Filipinos, and entertainers. Their Satanic music, jazz, and swing, result from marijuana use. This marijuana causes white women to seek sexual relations with Negroes, entertainers, and any others." -- Harry J. Anslinger, first commissioner of the United States Bureau of Narcotics