Best sounding Beethoven symphony LPs

Only one boxed set to recommend (see the end), but I'd first recommend you consider individual LPs to get better performances than any one boxed set provides overall.

Among more well known performances in good sonics that I'd recommend:

Sym 1 & 2, Marriner/ASMF, Philips 6500 113
Sym 3, Kleiber,Eric/VPO in mono on London/Decca
Sym 5, Kleiber,Carlos/VPO, DGG 2530 516
Sym 6, Walter/ColumbiaSO or Kleiber/Concertgebouw
Sym 7, Kleiber/VPO, DGG 2530 706
Sym 8, Norrington/LondonClassicPlayers, EMI EL 2705631
Sym 9, Solti/ChicagoSO, Decca 6BB 121/2 (or London)

Tacet Records has been working on a cycle of new recordings by Kajski and the Polish Chamber Philhamonic Orchestra and releasing them on vinyl. These are very nice, fresh performances in excellent sonics; don't be put off by the lack of big name recognition. So far, they have completed on vinyl the 1st and 2d on one disc, the 5th, and the 7th (Tacet L149, L157 and L164). These are special, imo.

For period instrument histroically informed performances, you might consider the series by Norrington and the London Classic Players on EMI. I don't think it was ever packaged as a box set.

For a box set, if you must, consider looking for the performances by Rene Leibowitz and the Royal Philharmonic Orchestra recorded in marvelous sound by Kenneth Wilkinson (Gerhardt, producer) for Readers Digest. This set often sells for under $25-50 on the used market. These are all very good performances by an excellent conductor, and the recording quality by Wilkinson is excellent.
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Get the Readers Digest complete set with Rene Leibowitz. Just make sure you get the stereo version...

Well I have some recommendations for complete boxed sets, but right up-front, I like my Beethoven clean, clear lined, and energized. I'm not up to deep, 'brooding' Beethoven.

Harnoncourt's set which blends the efect of the HIP but uses modern instruments. Scrubbed from the over orchestrated performances that were so common for so many years and are still highly regarded.

Bernsteins set - despite his general reputation for overblown distorted interpertations of a lot of music, in this set he gets the 'beat' - it is uplifting and energized. He did a similar set of the Schumann Symphonies with the same result. Whoda guessed. :-)

Vanska recent performances - a complete set of performances but not in a box set yet. You have to buy them individually. Excellent sound, SACD if you care, straight ahead performances. BTW I like them best with the volume up a bit.

Wand's set on RCA. Very tradition 'Germanic' performances.

I agree with Rushton, the best Beethoven is not found in sets. And as he has already recommended, BUY the Kleiber 5th! There is no other like it, IMHO.

I'm very fond of my Von Karajan, Berlin Philharmonic Orchestra 7th Symphony, DGG 2531 107. I think the detail is amazing. In fact I listened to it late last night through headphones and again this morning through my speakers after hearing the 7th used in the film "The Knowing."

Bernstein's boxed set with the Vienna Philharmonic (Deutsche Grammophone) offers both good performances and outstanding,up front sonics.