all depends on the athlete and the event, but 7 ten milers is more beneficial..... typically
people love to share their experiences, but thing is, everyone is different. One guy I knew doubled everyday, 4-5 miles x 2.... one was a workout, on workout days very intense, one easy. but always doubling. sometimes even 2-3 mile.... this guy was a an 800m all american in college and went on to success in the 1500 and mile after college.
Doubling helps w/ consistency if anything.... not necessarily aerobic development, but consistency and keeping the nuerons/muscles firing. This tends to benefit certain people more than others..... others as in kyle merber who now gravitates towards 80s on singles to get more rest between runs! try out different stuff and see what works, then trust your body and how you feel