Diapers pins! The vintage baby kind are my favorite--duckies, bears, and other animals. I've collected quite a few from eBay, and the points are infinitely sharper than the modern Dritz pins (although the Dritz pins are still pretty decent). If you go hunting for them, though, beware the made-in-China "novelty" diaper pins. These look the same as the old Reddy pins from the 50's, 60's, and 70's, but the points are total garbage. When possible, buy ones that are new-in-package so that you know they're the originals.
I don't find the adult-size pins necessary, but I have a few pairs. The ducky pins from Changing Times and Baby Pants are decent, but they have larger (diameter) shafts than the baby kind, and relatively steep tapers on the points as well, both of which make it more difficult to pin with them. The soap and hair oil tricks are definitely needed.
I've tried Snappis and I don't like them at all. Boingos are much more adult-friendly, as they're used one-per-side like pins. Snappis need to stretch between the two back corners of your diaper when they're pulled forward around your waist, and on an adult, those corners can be quite a distance apart! To use a Snappi, I found that I had to oversize my diapers quite a bit--wear an XL adult prefold instead of my usual medium. And then the diaper was so bulky that a single Snappi really couldn't create a snug fit. The only good experience I've had with a Snappi was when I used one with my Sweet Iris diapers, which are flats made from bamboo French terry. The fabric is stretchy, and makes up for the non-stretch of the Snappi!
(But you must only Snappi the non-loop side of the fabric!)
And some people like to wear two Snappis, one per side. But that's ridiculous. Real babies will laugh at you.
Back to pins: The nice thing about pins is that they're universally applicable to all cloth diaper fabrics. Biongos and Snappis are primarily intended for twill prefolds. They'll destroy regular terry (loops on both sides) and gauze, and have a difficult time holding onto some Birdseye and flannel fabrics. They're finicky! But they have their places. I do think Boingos are cute, and I use them from time to time.