While I have a fairly decent-size collection of paper punches, of the most-used in my stash is this scalloped circle from Fiskars:
It punches a 1.75-inch circle that's perfect for layering with other punches, buttons, or brads. I find myself reaching for this punch time and time again.
On this layout, I used it to create a grid (big surprise!) of layered flowers below my photo. The papers are from the Lily Bee Memorandum line, and I topped each one with punched butterflies, buttons, and rows of stitching.
I was able to incorporate eleven different patterns, without it looking too chaotic or busy. How? The linear arrangement of the grid and the fact that the patterns are similar in scale and color palette makes it look organized. The punched shape also plays a key role because it lets me showcase a small snippet of pattern, without totally covering the yellow background. The eye sees the shapes contained on this background as one large unit, rather than many smaller ones.
So what's your favorite go-to tool?