the bottom one is too bright. way too much white.. you cant really see much. The second one is amazing.. i like it alot, though i would suggest making the text just slightly more visible.. maybe 5% more opaque. The top one is so different i dont really know what to say lol. Its good though. I would suggest maybe lightening the render. Or darkening it. im not sure which
The bottom two look "pixely", if that makes any sense. The second one is still very good though. The last two also seem to have boring text, but you usually do that anyway, so it's more your style. I love the first one's right side, and the left side would fit right in if you lightened or darkened the render as kninja said.
A more common term would be that they're jagged or that they have jaggies. AA those edges. The third one is a bit too much of a yellow field to make it very interesting, and the second one is hard to read. The top one's fine, but the fourth one's the best. Perhaps you should round the bottom line by the text a little, though.