We use a lot of both...
I have not noticed that big of a difference from the two brands. We sell more Arlon 6000 XRP than 3M, but that is mainly b/c of the price increase.
I think we will be selling even less of 3M after I update our sales media kits with the new 3M pricing plans we are implementing. I think it is a very bad move by 3M to sell retail like they are getting ready to do very shortly...
So... I would say Arlon all the way after 3M purchased Original Wraps. But even before then it was very close to call, but the nod would have went to Arlon.
Arlon is a great product and will last for years on a vehicle. It is great for just about any type of vehicle wrap. I love the stuff... The prints look great on it (Printed w/ Roland Printers), the brands 3220 series laminate is great as well. It conforms to contours very well and we do not have to use a lot of Primer 94 b/c it sticks so well.