The 24" is going to be sharper because the pixels are smaller. Think of it as a box with balls in it. To get the same resolution between screens you'll need bigger balls in the bigger box. Whether it's good or bad is going to be up to your eyes. I have a Samsung 32" monitor with that resolution and while it isn't as sharp as my 27" iMac it's sharp enough for typing and game playing.
tl;dr The 24" will be sharper and smaller, the 27" will be easier to see small things on
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