Varig operates the Boeing 777-200 from Sao Paulo to Frankfurt, mainly because they codeshare with Lufthansa and they want both airlines to have about the same equipment level (comfort wise).
Out of the three routes you mention, I'd first of all eliminate the LH
346 one. Having flown the 346 about six times, the aircraft isn't anything to write home about. Seat pitch is 31 inches and legroom is simply ridiculous, although this seems to be normal in all Lufthansa intercontinental planes.
The 744 is a bit better in my opinion, the seat pitch and legroom being somewhat wider (still very average). You won't get PTVs either, but personally I like the 747 more than the 346. Service is usually good, yet it depends a lot on the crew you get. Besides, the 744 flight would be a couple of hours shorter, since the lay-over at GRU
is a mere 45 minutes, instead of some 3 hours.
As of Varig, they are a good airline, too. Their 777s all have PTVs, although they are not AVOD. They are currently serving EZE
with a mix of M11s and 737s, which are ok for a 2:30-flight. Service in Varig is good, but you also rely a lot on your crew's humour. Food tends to be about the same in both RG
I'm just writing out of my personal experiences. I'm a very frequent flier with LH
(Senator), and next July I believe I'll give a try to RG
. Both products are about the same, so it's up to you!