What is the best Mac for gaming?

None.

But if you really want to get one, get a MacBook Pro. M5 with as much RAM and Storage as budget allows

You'll want it specifically for the 10 core GPU and Ray Tracing support.

Beyond that, Macs are simply not made for gaming though they can run several games.

Many of the commercial games out there will require some form of jury rigging to work on a Mac through Steam and other layers to get them to work.

Games that are coded to natively run on Apple silicon include Baldur's Gate 3, Resident Evil Village/4, No Man's Sky, Stray, Factorio, World of Warcraft, Civilization VI, and many indie gems like Disco Elysium and Tunic

+1 on the idea that if gaming is your primary / only application, a Mac probably is not the best platform to buy. It's easier to find games for Windows PCs – at least, for ones that are equipped with high-end CPUs and GPUs, rather than cheap, low-end ones. But if you want a computer mainly for productivity, with a bit of gaming on the side, a Mac can be a good choice.

The version of the 14" MacBook Pro that has a plain M5 chip is the only Mac that has M5-series processors, so far. But in general, you get more GPU cores as you go from a plain chip, to a Pro chip, to a Max chip, to an Ultra "chip" (the Ultra being two Max chips joined back to back). Ultra chips are found only in a few extremely expensive Mac desktops – so that leaves Max chips as the ones with the strongest GPUs for any particular series (e.g. M4, M5).

How important it is to have a lot of GPU cores would depend on the particular game. E.g., if you are planning to run the X-Plane flight simulator with detail settings cranked up very high, you will be putting a lot more work on the GPU than if you were running a casual game.