Definitely metric! I like metric units because they are divisible into smaller units by a factor of 10 or 100, so it makes doing math easier (e.g. at the supermarket, when comparing prices). Also, I love the fact that 1 cubic centimeter of water = 1 ml = 1g. You can interconvert (at least with water) between different measurements tht way, and at least get a 'ball-park' estimate for other liquids. You can't do it that easily with imperial! Also, if knitting or sewing, it is much easier to deal with small measurements in millimeters instead of in fractions of an inch which can get confusing when adding.