Lufthansa vs United Business Class

I am considering going to New York and will be travelling back with a plan of getting an upgrade to Business (possibly).

I will be flying out MAN to EWR with UA however the return leg is fully booked already.
I think my best bet would be to fly back via Germany (FRA, MUC or DUS). I have never flown with either of these airlines so any shared experiences would be appreciated (nor have I flown through any of these airports, which is recommended?).

My options for the EWR to Germany leg are...
Lufthansa A340-600 (via MUC)
Lufthansa 747-400 (via FRA)
Lufthansa A340-300 (via DUS) - although I am not sure about this as it may depart too early for me
United 777-200 (via FRA)

Is the Business cabin / experience better on the UA 772 rather than LH's A346 or 744?
Otherwise how do economy class compare?
Thanks in advance.