Which PEX clamp is better?

I was looking at the PEX clamps and tools at the Hardware store. There are two types of clamps, and each uses a different tool.
One is solid ring which says it's copper, even though it's black colored. It appears that the whole ring gets crushed to a smaller size from the tool.
The other is silver colored and is supposed to be stainless steel. Those have a "nub" that sticks out and it appears that the nub is what gets compressed.
A store worker came over and asked if he could help me. I asked him which clamp type is the best. He said the stainless steel ones are best. But he was a young kid who did not appear to know anything about plumbing or any home repairs. The stainless steel clamps are considerably more costly, so I suspect he just based his answer on the price. (Assuming more expensive means it's better).
I've got a small plumbing project to do in the future and am considering PEX, but I want the best clamp, even if it costs a few dollars more. So, before I buy the tool, I want to make sure I know which clamp type is the best.
That guy told me that they rent the PEX clamp tools, but when I asked the hourly price, I may as well just buy the tool, and wont have to rush to get the tool back to the store to save money on the rental cost. One day's rental is nearly half the price of buying the tool, and I hate being rushed when I do any projects. I'll either save the tool for a possible future plumbing job, or I can sell it online when I'm done.
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