Basically you're looking for consistency somewhere around the mid to high 160s. Anything higher like upwards to 190 across the boards could mean it hasn't been driven enough with possible carbon buildup in the cylinders. I'd prefer a car with high consistent compression numbers rather than one with drastic changes like from 174 , 158, 169, 152, 169, etc etc. Look for consistent and mid to high 160s. If it comes across more than 170 across the boards, the engine should be in good shape.