Which is your fav Beethoven String Qt version?

I have the complete Quartetto Italiano set on CD, and one version of the Early Quartets Op18, Middle and Late Quartets (Vegh).

Not fully satisfied with the ones I had, I went looking to gather another version which would do justice to the complete cycle and I think I've found it with the Alan Berg version. Somehow this version seems to be paced "correctly" (I didn't fall asleep), and is well recorded on EMI. The music flows continuously and speaks to me. Highly recommended.
I love the classic "Hollywood Quartet" on Testament. Look into these, and you will be amazed to find out who the players are!

Happy listening,
The Tokyo String Quartet on RCA is fantastic. Brilliantly executed and profoundly expressed. Also beautifully recorded.The Alban Berg are also quite good but sometimes the first violin sounds strident and they sometimes over-project the music.
Guarneri for sure, especially the late quartets.
Tatrai, Vegh and Berg (for the late quartets)
Here's one on vinyl that few realize is a total delight - sonically and performance-wise. The Quartets Vol. 3 played by the Loewenguth Quartet on Vox Records (SVBX 544) three lp's with the purple "speakers" label. The playing is straightforward and sensitive, and the imaging / instrument separation is amazingly good - one of the best quartet recordings I have - mastered by Rudy Van Gelder, too.

Talich quartet on CD, very thoughtful with sound that sounds like them, try Op.59, #3. Bartok qt on LP.
I really wish they will issue some of these gems on LP, nowadays almost all modern classical music is only issued on CD/SACD.

Anyway, I continued to enjoy the Alban Berg version. I don't find the first violin strident in any way. I suspect it depends on what front end and power cables/conditioner you use.
I've heard the Aban Berg live several times through the years and have their Lps and CDs. Neither live nor in my system they sound the way you describe. I must be system dependent. I like them for their prefectionist ensemble playing. I adore the Vegh, also the old Budapest Quartet. I also like the Tatrai. Basically I find my self in the league with Rushton.