I use both, and am happy with both mobil 1 0w20(02 civic) and the amsoil 10w40 motorcycle(honda aquatrax f12x turbo jetski). Honestly, I think both are great oils. Reason I chose m1 0w20 is I wanted a real pao synthetic oil, not a group 3 like amsoils 5w20. Plus, the amsoil is overpriced. On the motorcycle subject, I can get amsoils 10w40 cheaper than I can get the mobil mx4t 10w40 by about 2 bucks difference per quart($6 vs 8). So, it all equals out somewhere.