I only run Amsoil in my bikes now. I am not an Amsoil nut, I don't run it in anything except my bikes.
The reason I run Amsoil is because of my 2006 Honda. I ran Amsoil in it when I bought it (used with 6K miles on it) but was tired of paying $10 a qt for oil. Not only is that more than I'd like to pay, but the Honda used enough oil that I'd have to add a qt between changes (race only bike). So, I changed to Castrol Synthetic MC oil. I instantly noticed a difference in the shifter feel. I could literally feel the shift dogs when shifting. I started missing shifts and it just felt bad. I dumped the Castrol and put Amsoil 10W40 MC oil back in and everything went back to normal. Because of this I run Amsoil in all of my bikes now. I still don't like paying $10 a qt but I feel it is worth the extra few dollars per oil change.
That said, I've never run any other oils and some others may be just as good or even better than the Amsoil. I found that I was happy with the Amsoil and just haven't felt the need to change ever since that one time.