Before I'd suggest any single quartet to the OP, I'd first ask him what kind of music he likes. I didn't find the late quartets intimidating; he might not either.
Some months have passed since I asked this question, but the only Beethoven string quartet I've heard is the first. To be honest, I find string quartets harder to approach than other configurations, maybe because of the fact that they're all string instruments and you don't have the tone color variety of a symphony or even a violin sonata.
FWIW, my favorite movement of the first Beethoven string quartet is the second movement. Also, the other day I was listening to the Smetana string quartets on TV and I found the first movement of his first string quartet ("From my Life") extremely compelling.
Other music that I like are mostly Romantic, Late Romantic and 20th century concertos and symphonies (Tchaikovsky, Mahler, Bartók, Ravel). As for chamber music, I'm fond of Chopin's nocturnes, ballades, barcarolle and his cello sonata.