To save some money, you could use the Rotella T 5w-40 synthetic, or the Rotella 15w-40 for even more savings but less smooth shifting.
I use the 10w-40 Amsoil synthetic and I also like the 10w-40 Maxima synthetic.
To save money I make my own semisynthetic, two quarts Amsoil 10w-40 and the rest Rotella 15w-40 from my ZZR600, and one quart of Amsoil and the rest Rotella for my cruiser, but there is some risk for doing this; although I am very happy with the shift feel, it seems better to me compared to all Amsoil 10w-40 for my cruiser.
20w-50 oil is for just summer use or an older engine more likely to burn and leak thinner oil. The air cooled engine owners will sometimes use 60 weight oil, especially for places like the Death Valley desert in the summer.