I'm currently using Amsoil's 10w30 synthetic (ATM) in my car now, but I'll be draining that out this weekend and putting in Motul 300V. I have nothing against Amsoil, just felt like trying out the Motul.
I've been using Amsoil 10w-30 ATM since I switched to synthetic for both engine and transmission two years ago. I use it for all my cars. For the NSX there is a slight improvement in shifting especially when the transmission is up to its operating temperature.