So we've seen sleepovers in both universes in the show (assuming you've seen Rainbow Rocks, and assuming you consider it 'the show'). But which universe holds the best ones? Let's analyse!

Sleepovers in Equestria (ponies)

Pros
▲ Easy to organise. Equestria's relaxed society means that ponies have less demands on their time, and are more hospitable. (At least, in my headcanon)
▲ Ponies can sleep anywhere with no visible discomfort. They still prefer beds, but they don't seem to complain if they have to sleep somewhere that isn't a bed.
▲ Equestrian buildings are bigger on the inside.
▲ Magic. If Twilight's hosting your sleepover and isn't freaking out, she can provide pretty much anything you need, even if she has to transform some helpless critter into a bed or something.

Cons
▼ Although ponies are on the whole friendly, they can also be fickle, and might allow a small quibble to blow up out of proportion.
▼ If Pinkie Pie is hosting your sleepover, you might not do a whole lot of sleeping. At least not until you find a way to send her to bed.
▼ There's not a whole lot to do. You'll probably end up playing Twister, and that's really hard if you're a pony (and really dangerous if you're playing against a unicorn).
▼ Ponyville and most other places in Equestria probably completely shuts down at night, so if you didn't get everything prepared beforehoof there's no running out to the shops. (In fact, this is sometimes the reason why ponies need to sleep over.)
▼ Rainbow Dash snores.

Sleepovers in the EQG universe (humans)

Pros
▲ More pajamas.
▲ EQG humans are really thin so you can get lots of them in one bed.
▲ Modern conveniences. Instant microwaveable meals, or pizza delivered to your door, even late at night.
▲ A vast amount of entertainment options, from television to video games to just watching random Youtube videos. And if you don't feel like that, you can even just go back to playing Twister and you'll probably be good at it too. Especially if you're an EQG human, because you'll be thin and have spindly arms and legs.

Cons
▼ Humans have busier lifestyles and so people might drop out of hosting or attending the sleepover, if you can even manage to arrange one.
▼ If Pinkie Pie is hosting your sleepover, you might not do a whole lot of etc. etc.
▼ Houses are smaller, and you might have to put up with awkward appearances by random family members.
▼ The most efficient way to stack humans in a bed is to put them at alternating ends, but that means that everyone's going to have to put up with smelly foot smell while they try to sleep.

Which do you prefer?

Eqg

ponies

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Well, I do believe that conclusively resolves this burning issue.