If you want the short version: buy the Epson EpiqVision Ultra LS800. It's rated at 4,000 lumens, which is enough to survive an afternoon football game with the blinds open, and its 0.16:1 throw ratio is the shortest of any ultra short throw projector you can actually buy. Push the console against the wall, drop the projector on top, and you've got a 120-inch picture in a room that was never supposed to have one.
That's the answer for most people. The longer answer depends on which of two very different products you mean when you say "short throw," because the category quietly covers both.
Two different animals wearing one name
An ultra short throw (UST) projector sits inches from the wall and fires the image almost straight up. It replaces a TV. A standard short throw sits four to six feet back, usually on a coffee table, and replaces a regular projector that would otherwise need to hang from the ceiling twelve feet away. Throw ratio is the tell: 0.4:1 or lower means UST, while something like 0.69:1 means you still need a little runway.
Neither is wrong. USTs cost more and look like furniture. Short throws cost less and travel. Pick your fighter before you pick your model.
The UST picks
The LS800 wins on brightness and placement, but it's not the best picture in the group. That honor goes to the Hisense PX3-Pro, a triple-laser design with Dolby Vision, IMAX Enhanced, and Google TV onboard. Its RGB laser engine covers a wider color range than the Epson's 3LCD system, and movies in a dim room look noticeably richer. At 3,000 lumens it gives up some daylight punch to the Epson, which is the trade in plain terms: Epson for bright rooms, Hisense for movie nights. The PX3-Pro also scales from 80 to 150 inches, so it grows with your ambitions.
The BenQ V5010i is the third UST worth your money, and it's the enthusiast's choice. Rated at 2,500 ANSI lumens, it's the dimmest of the three, but its triple-laser engine covers about 98% of DCI-P3 and BenQ's color tuning out of the box is the best here. There's a proper low-lag game mode too. If your room has real light control and you care about accuracy more than wattage, this is the one.
A quick note on screens: a UST on a bare white wall works, but an ALR (ambient light rejecting) screen designed for UST projectors is what makes these look like a $4,000 TV instead of a science fair project. Budget for one.
The short throw picks
The Optoma GT2100HDR is the sleeper in this list. It's 1080p, not 4K, but it counters with a 30,000-hour laser light source, a huge 4,200 lumens, and HDR10 input support. It'll take a 4K signal and downscale it, and input lag drops to roughly 8ms at 1080p/120Hz, which is quicker than most TVs manage. A 120-inch image from about four and a half feet, no lamp replacements, ever. For a garage, a dorm, or a backyard movie wall, it's the easy call.
The BenQ TH671ST is the budget classic, and it's earned the status. Around 16.7ms of input lag made it a golf simulator and console favorite, 3,000 lumens keeps it usable with a lamp on, and the 1.2x zoom gives you placement wiggle room that short throws almost never offer. The catches are real: it's lamp-based, so you'll buy a bulb eventually, and there's no HDR at all. It's also been around a while. It stays on this list anyway because nothing at its price has replaced it.
How to actually choose
Measure your light first, not your wall. A bright living room needs the LS800 or the GT2100HDR, full stop, and no amount of laser marketing changes that. A dim or darkened room opens up the PX3-Pro and V5010i, which both look better than the brighter options once the sun goes down.
Then measure your space. Less than a foot of depth means UST. A coffee table five feet out means the Optoma or the BenQ TH671ST and a few hundred dollars saved.
One wiring note, since this trips people up: if you're running a game console at 4K/120Hz, the projector and the cable both matter. Use a certified Ultra High Speed HDMI cable (rated for 48Gbps) for any HDMI 2.1 signal; an older High Speed cable tops out around 4K/60Hz. None of the 1080p picks here need that, but the 4K USTs benefit.
My money? LS800 for the family room, GT2100HDR for everywhere else.