I use
rectangular, not rounded,
labels.
They are easy to apply neatly using the following method.
Find a bar to lift your label the right amount from the base of the jar. (A frame topbar works for my labels and my 12oz jars ...)
Yes, it is easier to work at eye-level, or some close approximation.
Place the bar against the jar.
I hold the label at the top corners, rest the bottom edge of the label on the bar (so its level
), and gently touch the centre of the label against the jar. Then working outwards from the central contact line, working just to one side at a time, I smooth the label against the jar. Working outwards, rather than up or downwards, helps to prevent wrinkles.
Result of using the bar is that the labels aren't just straight, but they are also at a consistent height on the jar. Which looks good.
Just pick your bar (or other straight edge) to suit the height up the jar that you want.