These are simply the best. I've tried the cylinder with the screw top (too fiddly and awkward to use) and I've also tried Supple Nips (not enough suction and requires shaving the area for best seal).
The Nano Nips are perfect for newbies to nipple play as they provide enough suction without being painful. Simply squeeze the air out and push on for a firm seal. I use a little bit of water-based lube and they can retain suction for ages, even with some body hair. The base is slightly larger than an Aus 50c coin so it was bigger than I thought but it fits perfectly.
People who are more experienced with nipple suckers may find other toys from Oxballs to be more appropriate, but for me this is a great place to start. I chose the clear option so that I can see my stiff nips inside. Bonus - comes with a discrete, hard plastic carry case.