That's an interesting question. And it depends on the style of sweater. And how much time you want to spend on it. Some machine made sweaters use very thin yarn and thin 'needles', creating a very tight, clean looking sweater. This would take even the quickest knitter very long to make.
It is true that a machine will rarely make mistakes. But so do very experienced knitters. With enough practice, stitches can be made very even. And the hand knit sweater would be more expensive (if you include time of production and materials). But creating a hand made, one of a kind sweater is invaluable.
All in all, I think a hand knit sweater can be made of very high quality (with experience and knowledge (and a lot of time)), and the experience and product are well worth the extra effort.
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