That's a pretty broad question. Best in what way? Nbc has ONE show, F** has zip in HD, CBS has some really great looking stuff, (CSI), as does ABC. Can't get PBS but I hear some the stuff there is great. No one does local HD. PQ seems to be dependent on what the network serves up....
In Detroit, PBS (56.1) has great sound and pictures. NBC (4.1) is good also. Jay Leno (Tonight) is wide screen and good also. CBS (62.1) has good stuff. All six channels have mixed programing, but the PBS demo stuff is really a good place to show off your gear.
Detroit's PBS station WTVS has, IMHO, by far the best picture quality and strength of signal. The programming lately, with all the Smart Traveler series in Italy, and the "demo" U.S. travel shows that were on last night, are an absolute joy to watch. CBS looks really good too.
I would love to get WTVS, but it's not in the cards for me. I keep hearing about all the great stuff PBS has. I can get all the other Detroit stations quite well as well as the Lansing station but not PBS. Ch. 56 comes in crystal clear for me. Too bad they can't piggy-back their HD signal on the Ch 56 carrier rather than the Ch. 43-1 carrier. My best guess for my problem is co-channel interference. The FCC shouldn't assign the same freq. within hundreds of miles of each other.