So which a/c offer the best comfort? Which is more spacious... let me know...

For Boeing, the 777-style interior is by far the best. Boeing is also now offering it on new production 767s and 744ERs. Boeing has also recently redesigned the interior cabin for new 737NGs and 757s.

All Airbus planes have fairly spacious cabins.

As to which cabin is better (777 vs. A330/A340) for longhaul flights, I personally feel the 777 cabin definitely wins, and most people do seem to agree. That's not to say that the A330/A340 is uncomfortable- either the 777 or A330/A340 will provide a comfortable ride.

oh, and to add on to my previous post, here's an example of the 777 interior being applied to a new 767 and the great improvement it offers:

Before (old 767 interior): http://www.airliners.net/open.file/263184/L/

New (777 interior applied to 767): http://www.airliners.net/open.file/264880/L/