I would pick up at least a couple of 1ml, a couple of 10ml and a 20ml just to have around. Sometimes it is easier to go by volume (like if you are trying to lower nic. level in a
juice you didn't make) and they are pretty cheap on Flea-Bay. Other than that, pick up a hundred pack of disposable pipetes for transferring liquids around. Theoretically, if you have everything in dropper bottles you shouldn't need them but I find I use them all the time.
As far as accuracy, they can both be extremely accurate but I find it easier to be so with a scale.