I asked one of the guys at Natick Outdoor Store. I was contemplating paying a premium for Seaguar SENSHI.
He said that Berkley Trilene XL and Stren Original were the best selling lines in the US, depending on region. Trilene XL being more popular in the north and Stren in the south.
I don't know about best, but I've always had good results from Berkley Trilene XL.
I've also heard good things about Sufix Elite.
In truth any name brand should give you good service if you trim some off periodically (as bloomagoo stated), and replace it at least once a season.
Also, if your son is fresh water fishing for bass etc, 10lb line should be more than heavy enough.