My experiences differ. Since LH is kind enough to block the empty seat next to mine no matter what class I'm travelling in, there's always a good chance that this seat will remain free in C and F as long as my flight isn't completely sold out. Using that empty seat for "storage" is a bonus when working/playing with a laptop, so the 747 configuration can actually be more comfortable and convenient than the single seat on the 340. Regarding service, I'd say it depends more on the crew than on the a/c type, so YMMV.