Photoshop’s Rounded Rectangle vector tool appears like the ideal candidate for the task, until you realize that the edges it creates are blurry and inconsistent. Fortunately, there is a fairly well-hidden option that locks the Rounded Rectangle vector tool’s output to the pixel grid. Excellent. To enable pixel-locked drawing for the Rounded Rectangle vector tool, check the “Snap to Pixels” option in the Options bar. If you have “Snap to Pixels” turned off, drawing at 100% zoom achieves the same result.
The result is perfect roundrects, every time. The only downside is that the corner radius can’t be altered during or after drawing the shape. If you need a different radius, you’re forced to draw it again. It’s a shame the roundrect tool isn’t like Illustrator in this regard, where the up and down arrow keys increase and decrease the corner radius while drawing.
On the positive side, keeping your objects as vectors means that you’ll be able to resize the document and the corners will take full advantage of any extra resolution. There is one small caveat though: if you resize, you’ll have to do it as an exact multiple, or risk fuzzy non-pixel–locked edges. If you’re being pedantic about the results, you may notice that the antialiasing on the first half of each corner doesn’t match the second half — you’ll have to look carefully to notice, though.
For example, looking at the zoomed corner below, the start of the corner to the apex isn’t identical to the apex to the end of the corner (starting from either side). In practice, that probably won’t create any issues.