Stick to a full synthetic. You should use a 10W-40 or a 15W-50. I use Amsoil 20W50 or Mobil 1 20W-50. Both are expensive but I don't believe in compromising quality for price when it comes to oil.
Make sure the oil is JASO certified which means it won't mess up your clutch. The motorcycle versions of Amsoil and Mobil are certified.
