Plan ahead, and try to think of any/all possible future uses in the garage. Such things as--will you ever want to hook up an arc welder, or possibly fire up a kiln for fusing glass or pottery? If you only run a single line of 110 v., and later decide you really need 220 v., you will kick yourself for not putting in the heavier line wire the first time around.
I think a separate sub-panel in the garage is a must. Even if you never have the need for future, larger draw circuits, as it will save a trip back into the house to reset any breakers that trip. If it were me, I'd definitely want a dedicated appliance circuit (20-amp, 12-gauge wire) or two, and then at least one lighting and future electric garage door opener circuit (15-amp, 14-gauge wire), in addition to a 50-amp welding circuit. Pulling them all from the new sub-panel, leaving some room to spare for future circuits. And don't forget to apply for a permit, if required by the AHJ in your area.