Moen uses the same 1225 cartridge (pictured below) in every single lever faucet they make. That's not just kitchen faucets, they also use it in all of their single lever bathroom sink and Tub&Shower faucets, and have for many years.
The one you get with the faucet will be brass, but any replacements they send you will be plastic like the one above.
It's what turns on, shuts off and regulates the flow of both hot and cold water. So, since this part is the same on all Moen single lever cartridges, then it's not reasonable to say that the 1225 cartridges used in the expenive faucets work any better or more reliably than the 1225 cartridges used in the cheaper faucets. They're all made the same.
But, there are other things that can wear out on a Moen single lever faucet beside that cartridge. If your spout swings from left to right as most kitchen faucet spouts do, there's undoubtedly an O-ring in there and probably two. It's possible that Moen uses two O-rings in their more expensive faucets in places where they only use one in their less expensive faucets. I don't know if that's the case or not as I've never taken the time to find out since I don't buy $300 kitchen faucets for my apartments. I just know that the cartridge that controls the water flow is the same.
It'd be a simple matter to find out, tho. The literature inside the box on Moen faucets will have an exploded view of the faucet in it. Just ask the guy at Home Depot to photocopy those drawing for you, and compare them to see if the more expensive faucet is built any differently than the less expensive one.
Don't get me wrong. I like the Moen 1225 cartridge, and many people do. It provides many years of trouble free service.
Delta uses a stainless steel ball and spring loaded rubber seats in it's single lever faucets. It's a completely different system (and is seen below):
In Delta single lever faucets, moving the handle causes a hollow stainless steel ball to rotate in different directions. The water comes through spring mounted rubber seats that press against the ball. There are holes on the ball, and as the ball turns, a larger or smaller area of hole is expose to the seat, and so more or less water flows through that seat.
Asking which is better, Moen or Delta is just like asking whether Chevy, Dodge or Fords are best. There are people who prefer one over the other, but if you ask me, both provide good service. I have no Delta faucets in my building, but my sister has a Delta single lever kitchen faucet and she's happy with it. I have a Moen single lever T&S faucet in my bathroom, and I'm happy with it.
If the world were perfect and only clean water flowed through your faucet, you would seldom ever have a dripping faucet. But, what I've noticed is that whenever I see a City of Winnipeg Truck doing any work in my neighborhood, I often get a spat of dripping faucets in suites after that. The correlation is simply too strong to ignore. I believe that every faucet would provide much more trouble free service, but a big cause of problems is stuff like sand or other foreign material that gets into the water supply pipes when they're being serviced. And, no company has produced a faucet yet that will tolerate stuff like sand or metal filings in the water.
I expect Delta uses that same stainless steel ball system in all of their single lever faucets, but I don't know that for sure.