It doesn't make any difference one way or the other. The only ones that claim it makes a difference are the tire manufacturers and the tire dealers. The only difference it makes is in the thickness of yours and thier wallets. They prefer that yours be as thin and light as possible while thiers is as thick and heavy as possible.
David M. - actually that is a tough call. Not so much in what front tire I think is best (IMO, it's clearly the G709), but when it's all said and done, you still have the E-3 on the rear, which I personally have found just doesn't cut it on the 1800 The rear E-3 is still going to be very noisey and in wet weather, I still found the rear Dunlop broke loose on wet pavement, so I didn't like it a bit. I couldn't get my rear E-3 off fast enough following a wet 2500 mile trip last year, so I don't plan on revisiting that rear tire ever again.
IMO, get the Stone G709 front and then ask the question again.
A lot of guys run a small rear tire on the front, Such as a 130/70-18 Michelin rear. Gives very good life and they handle just fine. Then install a good car tire on the rear and you have a husky set of tires that will take a pounding.
I am another "couldn't vote" as I would not have an E3 on the rear. It was the worst rear tire I have had on a GL1800 (haven't tried Avon). An E3 on front is OK, but it unnerves me a bit not having any "chicken strips" as I run it out to the edge of tread. Although, I will put an E3 on the rear before I put a D250 or Avon on the front because of tread design.