If the console in your house is a Switch 1, buy Mario Kart 8 Deluxe - it is the only one of the two that runs on it. If you own a Switch 2, buy Mario Kart World
This comparison is decided by hardware before it is decided by anything else, and that is unusual enough to state in the first line. Mario Kart World is a Nintendo Switch 2 game. It does not run on an original Switch, there is no downgraded version, and no amount of wanting it changes that. Mario Kart 8 Deluxe runs on both. So for the large majority of households - the ones with a Switch 1 on the shelf - the question answers itself and the rest of this page is interesting rather than useful.
For a Switch 2 household, buy Mario Kart World. It is the newer game, it takes up to 24 players onlineagainst 8 Deluxe's 12, and the local cap is the same four on one console - so you lose nothing on the sofa and gain a great deal online. And if the room you are buying for has a PS5, an Xbox or a PC rather than any Nintendo hardware, neither of these is the answer: Sonic Racing: CrossWorlds is, because it is the only current four-player split-screen racer that runs on all three and crossplays between them.
Where the two are identical, which is the part that surprises people
The couch experience is the same number of people: four, on one console, from one copy. Nintendo's listings put the local cap for both at “Single system (1-4)”. If your entire reason for buying a Mario Kart is that four people are going to sit in one room and race, the newer game buys you nothing on that specific axis, and the older one is substantially cheaper. That is a genuinely unusual thing for a sequel, and it is the most common misunderstanding this page exists to correct.
Both are also same-platform only. Neither crossplays with anything, so a friend on a PS5 cannot join either of them - the list of games that are not cross platform carries the Nintendo racers for exactly this reason, and the crossplay hub is the page to read if a mixed group is the actual situation.
Where they differ, in order of how much it should move your decision
One: the console. Decisive. Mario Kart World is Switch 2 only; 8 Deluxe plays on Switch and Switch 2 both. If you are buying for someone else and you are not certain which machine they own, buy 8 Deluxe - it works either way, and that risk asymmetry is the whole argument. Our Switch 2 page covers what the newer console adds beyond this one game, including GameShare.
Two: the online cap. 24 against 12. Doubling the online lobby is the clearest concrete upgrade in the newer game. Whether it matters depends entirely on whether your group plays online at all - most households who buy a Mario Kart play it in one room, in which case this changes nothing.
Three: price. 8 Deluxe has been on sale for years and World is the current flagship, so the gap is usually large. Both rows in the table above carry a live price with the date it was checked rather than a number we typed, because this is the variable most likely to decide the purchase and the one most likely to move between now and when you read this.
Four: how much game there is. 8 Deluxe has had years of additions and is enormous for the money; World is the newer, larger-in-ambition design. Neither of those is a specification we can quote from a listing, so treat it as what it is - an editorial read, not a measurement.
Buying one as a gift? Read this paragraph twice
The single most expensive mistake available here is buying Mario Kart World for somebody who owns the original Switch. It will not run, and a Mario Kart is exactly the kind of present bought by someone who does not follow console generations. If you cannot verify which machine is in the house, Mario Kart 8 Deluxe is the safe purchase - it runs on both and it is cheaper. Our family gift picks and the under-$100 list both carry these two for that reason.
