1/2, 3/8, 1/4 is the drive size, this is less important than the torque range in the applications most people will be using them for - i.e. if the bolts you need do torque to 25Nm a torque wrench that covers 40-200Nm isn't going to do it regardless of its drive size. It's unlikely you will get a 'one size fits all' wrench, I have one that does 10-80Nm and one that's 40-200Nm. To give you an idea my caliper bolts, pinch bolts, etc are 25Nm so they are the smaller 10-80Nm wrench but the axle is 110Nm so is the larger 40-200Nm one. Generally the higher the torque rating of the wrench the bigger the drive will be but at the lower ends there will likely be a choice.