A Word of Warning: Watch your seats on the codeshares.

The family and I just got back from a (Paid) Business SFO-TLV r/t on CO. The first flight was on UA, booked on 016 stock by the UGS desk. On the return in TLV, check in took 45 minutes at the desk as CO had completely lost our seating assignments. I looked up the reservation on ual.com mobile, which still showed our correct seats that had been held since last October, but the staff said no seats together were available. In their words "It's not our ticket, it's a United ticket-- it's not our problem" (verbatim). So the four of us were all spread around the cabin, on both flights, as some fellow passengers were a little less than understanding (I'm looking at you, 3E on CO 448!)

All in all, the service the whole way back was horrible (But that should be a different thread). What is amazing is how the airlines still are not able to talk with each other. So, go ahead and book the code share. Just don't expect anything to work properly. Check, double check, and double check again... then do the same with the other airline.