I have four cars/trucks, two boats (one I/O and the other 50HP OB), one generator and a large selection of mowers, snowblowers, etc. For the last 15 years the only oil I use is AMSOil. If you plan on keeping your vehicles a while (my SRT will be in my garage 20 years) consider it. It is not cheap to buy but seriously protects your equip. However, if you plan on trading in 3 years, Mobil 1 is good enough.

Here are some charts showing all the leading motor oils. I plan on changing my SRT oil according to oil tests.

http://www.amsoil.com/lit/g52.pdf