Oh man, I feel your pain. I used to manage a little plaza, and it felt like every Monday morning was a fresh crime scene—slats ripped off, tags everywhere, or the entire thing unbolted and thrown into the bushes. The frustration is real. You don't just want a bench; you want a slab of invincibility that laughs at a baseball bat.
After way too much trial and error (and replacing cheap stuff that cracked like candy), I've learned the hard way that material is 90% of the battle. Avoid wood and hollow aluminum like the plague unless you like constant repairs. What you need is either monstrously heavy steel or recycled plastic that's basically indestructible.
For a bench that can truly "take a beating," my first pick is always a coated steel bench with a tamper-proof mounting system. Specifically, look at something like the Ulti-Matte Steel Bench from manufactures specializing in high-traffic urban furniture. The bench itself is usually built from heavy-gauge, galvanized steel with a thermoplastic coating. Key is the mounting—go with in-ground surface mounts that use security screws, or better yet, pour a concrete pad and anchor it with internally locking bolts. A crew with a crowbar will need half an hour and a lot of noise to take that thing down. Graffiti wipes off the coating with a standard remover without eating the color. Some models like the Stomper from Groundwork Industries have interchangeable flat slats, so if a psycho *does* manage to damage one, you replace just that slat instead of the whole bench.
If the look of steel is too industrial for your neighborhood, my second-best recommendation is recycled plastic lumber (RPL) benches, and I don't mean the cheap fake wood. I'm talking about solid, 4-inch-thick planks made from compressed HDPE, like the stuff from Poligon or DuMor’s Site Furnishings line. These things are virtually impervious to moisture, insects, and spray paint (it beads up and you can scrape it off). The color runs all the way through, so if someone takes a knife or a lighter to it, you just sand out the scratch and the color is still there. Go with a cast aluminum or heavy stainless steel frame underneath, and it's not going anywhere. I've seen a car bump a recycled plastic bench at low speed, and the bench got a scuff while the bumper fell off.
My final "bunker" pick for absolute war zones is a solid concrete bench, but the kind that comes as a single, unified piece with legs cast right in. Something like the Wishbone or Ranger models from Dura Art Stone. Yes, they are a beast to install (usually dropped via forklift), but they are literally too heavy for a group of people to casually flip over. No moving parts, no slats, no exposed fasteners. The only thing a vandal can do is paint it, and if you seal it annually, a pressure washer handles the rest.
Don't underestimate the fastening. Buy security anchor kits rated for the material of your walking surface. No exposed hex bolts. Ever. And if you can, pick darker, speckled colors—they naturally hide etching, gouges, and shadow tags better than smooth, bright surfaces.
I know these options cost more upfront than the $300 box-store special. But think of it this way: after one season, you won't be paying a crew for overtime removal of the twisted carcass of a cheaper bench. You'll just be sitting there with your coffee, enjoying the view. Cheers to that.