All else being equal if you have a choice which do you prefer and why?
Plastic caliper pistons or steel?
I have 2 sets I blew apart, blasted in my cabinet ( currently loaded with glass beads) powder coated them and rebuilt with new seals and pistons. I built 1 set each with steel, and plastic, pistons. All pistons I put in upon rebuild were brand new . Plastic were Carlson brand, steel ones were napa united brand. the napa ones came from eBay and were definitely more "shelf worn" / faded.... And double boxed at that. The Carlson ones were from rock auto. And unfortunately Chinese manufactured
I liked $9 ea from eBay for the steel pistons, instead of $30 ea off the napa shelf down the street.
I got 2 of the last 3 plastic ones that rock auto had last week. From there plastic vs steel were within $1 ea of each other. $11 -12 ea.
I know what I remember hearing 30-40 years ago like "don't mix/ steel on one side and plastic on the other side of same vehicle". Then all of a sudden that wasn't taboo anymore, a mix match was supposedly "fine". I don't know what changed there.
I know one thing
With new seals and dust boots, the steel pistons went back past the seals and seated down to the bottom much easier than the plastic ones did.
I did put a chunk of 2x4 in there and used air to apply each piston and they both seemed to react equally compared to each other, no fight/ struggle for the plastic ones to apply vs the steel ones on the bench compared to what a pain it was to get the plastic ones past the bore seal compared to how the steel pistons went back...
The last calipers I rebuilt before these was about a year and a half ago for my son's 72 fury. Remans weren't available anywhere at the time. Prior to that was probably 35 years ago when I worked at the 1st of 2 sears auto centers I worked at. Back then every car that came in for brakes automatically had their calipers and wheel cylinders rebuilt or we wouldn't take the job. The only ones that got replaced vs rebuilt were ones the bleeders busted on.

In my case both sets ive recently rebuilt, are for a d250. I only need 1 set right now but figured it's best to rebuild both sets now if only to keep the " spare" set from rusting anymore until I get to use them
and between me and my son, they will be used / either on my d150 or d250 or his ramcharger.
I think I'm gonna use the ones I put steel pistons in on the d250 first.

I have to do the fronts on my 76 Dart Sport.
Not sure what I am going to find.
I hope I can find some decent parts to put it back together.
I am sure I will need a master cylinder as well.

_________________
Hyper_pak

That discussion would've been relevant when all things were equal, maybe(!) as late as 15 years ago or so.

With the severe decline in auto parts quality across the board – very bad for parts for recent-model cars, much worse for new parts for old cars – pretty much all other questions are moot other than "what can be had in the best quality?".

There are theoretical benefits to phenolic ("plastic") pistons. No corrosion, less heat transfer to fluid, lower mass. But none of those benefits comes true in practice if the material and/or construction is shoddy.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

Funny that in all my life I have never rebuilt a caliper. I just buy new, and I have never had a single one stuck, leak,or otherwise not function properly. I was probably just lucky.

_________________
2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

By that I was meaning same car same engine same usage same pads same tires etc just
the only thing different is calipers with which piston material

My answer doesn't change much. Even if you could really have your pick of equally-good-quality metal vs. plastic, any practical difference in realistic terms (noticeable benefit or drawback) would be so unlikely and minimal as to vanish off the list of things to spend significant time thinking about. Good quality caliper pistons, whatever they're made of, generally don't make much trouble.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

The steel napa ones I got from eBay definitely aren't new stock. So I feel good about that , hopefully they're old enough for QC not to be an issue. The plastic carlson ones from rock auto though were marked "made in China" in pretty big print on the box, the steel ones went back in the bore past the square cut seal so much easier than the plastic ones did so there's that....the ones I did first that I built with the plastic pistons. were also the first pair I powdercoated. They didn't come out as nicely coated, as the 2nd set did// which got the steel ones .... I'm probably gonna use the 2nd set just because of that even if all were plastic or all were steel.... And put the other ones on a shelf for " next time" one of our 3 trucks between my son and I that use these particular ones, needs a set. Thell collect dust in the meantime in the attic but won't rust in storage anyway....
Since I took this truck down to the bare frame and blasted /painted that and coated a bunch of other small parts before going back on, I'll use the ones that the outside of, looks better on
I definitely know that that isn't code for "nice paint makes em more likely to be good" haha.