There's no one size fits all answer to this, it depends on your circumstances, what you will record, how you will record, how many tracks a ta time, what your budget is, what gear you have now, etc. Give more details for a more considered answer.
Some general truths are that a low cost mixer will have very little money allocated into each preamp, vs a standalone preamp having it's entire build cost into it's one or two preamps (more in some cases, but you get the point). So, standalone preamps tend to be better than the preamps in a low cost mixer. But if you need the extra functionality of a mixer, and I think pretty much everyone should have one, then a mixer is a good place to start, and the standalone preamps can come later.