The first difference I told my friend about Clarity (which none of them know) and Prius Prime is Clarity is more an Accord family sedan, Prius family is more a Corolla compact, they are of different classes.
After tax credit and rebate, they're about the same price and Clarity offers more goodies, choice is simple to me.
But not everyone needs a family sedan. If you want a smaller car to go around the city, better MPG and no one question your choice of car, Prius Prime is the safe choice.
(I'm not kidding, if you got Clarity and had problems, you would hear words of why not getting a Prius...)
(When I said I was going to buy a PHEV, my friends would only say Prius. That's everyone's go for car for hybrid. I'm sick of explaining why I didn't get a Prius)
Before I bought Clarity, I'd been looking at various PHEV including Ioniq, Niro, Prius Prime and Clarity.
Basically Prius, Ioniq and Niro are all in the class of Civic and Corolla by its exterior size and interior materials.
Since we need to fit a baby stroller (folding seat down is not an option as we have car seat), all of them can barely fit one and leave us very little extra space.
I'm never fond of Prius (any trim) and in fact, I hate its super large screen. Don't need something screaming I'm different.
Both Ioniq and Niro are good and better warranty. I was settling on Ioniq because I prefers its look and interior is better than its sibling Niro. Niro doesn't have larger trunk as a CUV.
But since our purchase plan changed, so I got more time to wait for Clarity PHEV to the market and it basically checks every our requirements.
Last but not least I value driving experience more than those MPG values. Cars are built for a purpose and sometimes you need to sacrifice MPG. I have a Miata for my daily drive and a Wrangler for rough road trips and home depot, now a Clarity for my wife and family.