Both kinds can irritate if overused, while both can also not work well if under used. Many products with chemical exfoliants don’t have enough actives to actually do much, while ones that have quite a bit might irritate those with sensitive skin. Mechanical scrubs vary in coarseness, so some might be too much for some people. Plus a mechanical scrub should not be used every day. The upshot is knowing your skin and what it can handle. If sensitive, a very light mechanical or chemical scrub might be all that you can take. In that case, consider just scrubing a bit with your washcloth, it does the same thing! If you aren’t sensitive, you likely can happily use either the good chemical exfoliators or a heavier mechanical scrub.

Personally I like both. I use mechanical scrubs once or twice/week and retinol or glycolic acid on and off. But unfortunately I am a bit sensitive to retinol, which is one of the best exfoliators and anti-aging actives.