I used to work in a chemical processing plant that used hydrometers, refractometers, and auto specific gravity sensors. Honestly, they all work. If you can spare sample for a hydrometer, go for it. I personally love my refractometers-it requires very little for a sample and is dead on to 0.0X. I brew 1 gallon batches, so I appreciate not having to draw a sample for a hydrometer reading from my carboy.