The easiest to operate (for me) is the hand held one that cuts the top off from the side of the can. It leaves a sharp edge but as long as one is careful, it is OK. I don't have enough gripping strength to operate the other sort any more. They are not extremely expensive.

It was kind of expensive, but I have a on-the-counter can opener that breaks the seal on the lid so you pull off the entire lid, no blade, no jagged edges to worry about, no possibility of little metal filings falling into the can after opening. I got it at Walmart, I think it was $35, it's a Hamilton Beach. I consider it one of my best investments.

I bought one for my son as a house warming gift. He thought I was crazy to get him one, he was using a hand opener, but now he says it's the best thing ever and he recommends them to all his friends

I have one of the small openers, a little larger than a computer mouse. I like it.
My hands are weak due to several surgeries and this requires no strength to operate. I keep it handy in a drawer so its out of the way.

I love the cans that have the pull open tab on top. Pretty soon maybe all cans will be this way!