I use whichever one has no ethanol in it. Around here it depends on the station you go to, some are 91 that have no ethanol and some are 93 that have no ethanol. I just got rid of my Cruze, which was the LS 1.8, and I've noticed it runs 1l/100km less (6 MPG better) than regular gas, which around here contains 10% ethanol. I had been doing this for the past two year, with no problems. We still have my wife's Cruze, a LT 1.4T, and she's been doing the same.