To me the "best" take-along multi-tool is also one of the lightest and cheapest, Park's MT-1 "dogbone". It has 3,4,5,6 and 8 mm hex keys, a small flat head screwdriver and 8.9 and 10 mm box wrenches. All of the larger hex keys and boxes are oriented to have adequate leverage and it only weighs 40 grams and costs about $12.

It's certainly not a shop level tool and not for routine use but it fits in any pack or pocket and, along with a small chain tool will do nearly any roadside emergency adjustment. Why it isn't more widely known is a mystery to me.