To my mind, either Joseph Keilberth's 1955 set or Hans Knappertsbusch's 1956 set (in its Orfeo incarnation) stands at the top of the heap. Keilberth has stereo sound, which - while not modern digital - is serviceable. Keilberth, too, has a more energetic and driving approach. Knappertsbusch, marginally slower (15h11m24s vs. 14h03m07s) than Keilberth, has a more monumental and epic approach - with largely the same cast. Of the "Golden Age" sets, these two are really the major entries from Bayreuth. Solti needs no introduction, but I personally find Hotter to be a bit past his prime for the recordings. He can be heard in better - read, glorious - voice for Keilberth and Knappertsbusch. Solti's 1983 Bayreuth performances, available from "informal" sources, are - for me - the best Solti outing, even if the casts aren't as titanic as they were in Vienna. Von Karajan's set is fine for what it is, but it is not a first or even second choice set. Böhm and Boulez are both acquired tastes. They have roughly identical timings, with Böhm edging out Boulez in, I want to say, three of the four evenings. If you like speed in Wagner, then toss a coin. I find the Boulez recording a little distant, but such things are trivial concerns. Janowski is a contender, but his cast doesn't always satisfy me (Altmeyer, in particular). Levine is too slow. That's a difficult concept in Wagner, but Levine manages to find it (at 15h20m43s). Haitink has his moments, with Tomlinson's nasty and bleak Hagen in Götterdämmerung, but I wouldn't go out of my way to get the whole set.
At the end of it, I would say that Daniel Barenboim's Bayreuth set is the best of all worlds. Reasonable timings, a solid orchestral concept, and a cast ranging from good to wonderful (Tomlinson's Wotan/Wanderer). Throw into the bargain the Festspielhaus acoustic and modern digital sound, and you have a winner. So, you need two sets:
1. Keilberth '55 or Knappertsbusch '56 or Solti, and
2. Barenboim.
