My recommendation is a digital/electronic scale. They have fewer moving mechanical parts, which are generally what cause inaccuracy and failures. Perhaps the most important feature to look for is one which comes with a physical reference weight you can use to check and/or re-calibrate the scale. Without that how confident will you be that it is still within spec one or two years from now? Also be certain it has a 'Tare' function (most digitals do, mechanical scales do not). And know in advance how large the things you need to weigh are and how you will physically put them on the scale platform and not have them shift around. Dealing with a large retail site such as Amazon means you can expect the warranty to be honored if you have problems.
Try to find a unit with one more digit on the display than you think you need. Reading down to 1 gram isn't good enough, 0.1 gram is marginal, but 0.01 gram is probably adequate in practical terms.
