Polymer. Having shot both. Lighter, cheaper, almost/just as, accurate. Carry or not.

Honestly, 6 of one, half a dozen of another. For most people, they will never shoot out a gun that is polymer vs steel. Now, with the military, steel guns last longer and is a preferred base until recently. Polymer has gotten stronger and with component chassis like the SIG 250 or 320, polymer has begun to make inroad because of their price and weight. Also, if you shoot a larger round, the extra weight of steel may help you with the recoil like with a 1911 for 45 ACP.
Pick a gun that is comfortable to use, a weight you are comfortable with, a caliber you can handle, AND will carry on a regular basis. Invest in a good gun belt and holster and decide if you want in the waist band or outside. Good luck.

Lot's of good answers and comments here. I've own a few of everything...steel, alloy (aluminum) and polymer frame guns. The slide of most polymer guns still ride on steel frame inserts and the frame itself isn't really contacted that much. So I don't really buy what you're being told. I have two Sig P-320s with polymer frames, both are 9mm. One is closing in on it's fourth case (4000 rds.) and the other has maybe 5-600 rounds through it and after I read this question I field stripped both for inspection and I can't see any difference in wear or loosening in the frame to slide fit. My older compact 320 has had exactly one failure to eject with some steel case ammo...but only one. My little sub-compact has NEVER had a single failure of any kind. I see no reason why these plastic-fantastic pistols shouldn't give you many years of reliable shooting.

I have steel framed CZ's ,1911's ,2011's and a couple plastic M&P pistols. They all have thousands and thousands of rounds through them. They are all extremely durable...the 1911 and 2011 require more attention to running smooth.
For me the CZ 75 has been the most dependable and is heavy which cause less felt recoil than the M&P.
Just about all name brand pistols are extremely reliable and last for thousands of
Rounds before any issue arises.

Not any truth in that. The points raised would be valid if you were talking about a "service" type weapon. Even then most policing agencies use Glocks, so apparently they don't believe that either.

They are trying to convince you of a lie and I'm not sure why? Maybe they have that opinion, or own them inferior old firearms and want some company or validation from you. But don't believe them. I think an overwhelming majority would rather have a lightweight firearm any day. As long as cracks didn't occur while manufacturing was in process, a future crack is extremely unlikely. Your steel slide is way more likely to ware out before your polymer frame. Get the modern improved firearm, you won't regret it.

The steel frame guns I have had remained more accurate and reliable as they accumulated rounds through them but for normal use there's little difference. The plastic frames do help mitigate recoil better. Just remember to buy quality because if you are going to shoot either type of frame enough to wear it out the money you'll spend on ammo will greatly surpass the cost of the most expensive pistol you could buy. Steel frame pistols like CZ or Sphinx or plastic frames like Grand Power X-caliber and HK are good choices.

I'm with David on this, I carry both in my line of work. Love my stainless .45 but it is like carrying a brick on hip, Now my polymer is so light weight I don't realize I am carrying it till I hit it. I have never had a issue with either gun and as long as you take care of it, you should almost never have a issue.

I have both and love both. I do worry more about my steel guns getting banged up and scratched. I've been fortunate and haven't had any malfunction with either but I do clean and maintain them. They steel guns can be heavier witch can be good for recoil but cause fatigue during a long session at the range. I agree with David G and I would do some research on the brand and steer clear of brands with a lot of complaints about customer service combined with malfunctions. My recommendation would be to pick a couple guns of each type that appeal to you and make some calls to ranges and see if you can find them for rent. You'll know more about how you feel about the two types once you've fired them. I think a comfortable gun in your hand is key more that the material it is made of. I know its not a definitive answer but I hope it helps you in choosing a gun.

I've found that they both have pluses and minuses. Steel is, in my opinion more durable and with that I would say less likely to get damaged and malfunction. Polymer frames are lightweight and more comfortable to carry. With that said I've never had an issue. Take care of your firearm, try out many and make your own opinion on which you would prefer. I wouldn't worry about the frame style vs reliability. I would focus more on avoiding brands with poor track records.