Some of the worst I ever saw were:
WLWI/13 (now WTHR) Indianapolis IN circa 1970. They were the very-weak ABC affiliate at that time - a very poor station in a Top 25 market. No redeeming features whatsoever in their newscasts under Crosley/Avco ownership, and a horrible signal to boot. The only guy worth watching was some Ball State grad named Letterman doing weekend weather. I hear he went onto bigger and better things.
WAEO-TV/12 (now WJFW) Rhinelander WI circa 1971. Even for a very small market station (it's always been the Wausau-Rhinelander market, but they really didn't start serving Wausau until the '80s), this was low-budget. The anchors were the sales director on news, the program director doing weather, and another sales guy on sports. No news film/tape unless the story was about then-Rep. Alvin O'Konski, the local congresscritter. By some strange coincidence, he also owned the station. ;D
WBBM-TV/2 Chicago circa 1972. This was about a year before CBS paired up Bill Kurtis and Walter Jacobson and turned it around. It's not that their anchors were bad - they had John Coughlin doing weather and Burnt Hamburger Brent Musburger on sports. But that set looked like it had been shipped down from Green Bay - very crude by network O&O standards, even of that time. And it was called "TV 2 News" instead of "Channel 2 News" - a very weak presentation for the #3 market. Footage of this era on WBBM exists.
KPAZ-TV/21 Phoenix AZ circa 1974. This was pre-TBN, when they were still a half-secular, half-religious independent. Probably
the worst newscast ever - this was small-market UHF-from-1953 stuff, except that it was in color. The anchorman was a Wally Cox look- and sound-alike who made Ted Baxter seem like Walter Cronkite by comparison. The weather map was a National Geographic US map mounted on the wall, with a clear plastic overlay so the weather-guesser could write on it with his magic marker. Their only saving grace was sports. The sportscaster actually attempted to be professional, and he also did Phoenix Giants play-by-play on the station. It was also the only 5 PM newscast in Phoenix at the time.
KTVK/3 Phoenix circa 1974. Decent anchors except for the old lady doing weather, but the set was horrible and the graphics were well below their competitors at KOOL, KTAR, and even then-indie KPHO. Just a very small-market feel for a network affiliate in what was then somewhere around Market #35 or so - even if that network was ABC.