It mostly depends on how big you are. I'm not very familiar with Delta's product but with UA, Economy Plus is the exact same 18" wide seat and service as regular economy with the addition of a few extra inches of leg room. For me, it is a no brainer as I am tall. Those extra inches are the difference between being merely uncomfortable or completely miserable for a long flight.

ANA will have somewhat better service and food but has among the tightest regular economy cabins in the business on the 777 with 16.5 inch wide seats and 31 to 34 inches legroom. That is unless you can score the 787, which has roomier economy seating.

You might want to check your options on http://www.seatguru.com/ .