I am buying three Round Trip Tixs from DFW-BOM (Bombay, India) around 18,500 miles for round trip.
I am newbie to world of mileage. Which program is better NW or Delta? I know they both accept each other milage.

I also know that but not sure or know how to do it!!!
I can open one mileage account on my name and add all the milage for other 2 ticket to my account? Is this possible?
Any their any annual fee or other fee on either program?
I am buying tickets from a agent because they quoted me the lowest price. So what would be the procedure I can all the miles into one single account.

I am newbie so excuse my stupidity