Ποιος μιλάει ελληνικά καλύτερα από όλους;

Ποιος means who? and it is the subject of the sentence, so it appears in the nominative case.

• Ποιος = masculine singular nominative
• If you were asking about a female specifically, you could use Ποια
• If who were the object instead of the subject, Greek would use a different form, such as ποιον

So here Ποιος is correct because the sentence is asking who is speaking.

Μιλάει is the 3rd person singular present tense of μιλάω / μιλώ, meaning he/she/it speaks or is speaking.

In this sentence it matches Ποιος:

• Ποιος μιλάει... = Who speaks...

A learner may also see μιλά instead of μιλάει. Both are common in Modern Greek:

• μιλάει
• μιλά

They mean the same thing here.

In Modern Greek, names of languages are normally written with a lowercase letter, not a capital letter.

So:

• ελληνικά = Greek
• αγγλικά = English
• γαλλικά = French

This is different from English, where language names are capitalized.

Here ελληνικά means Greek as a language.

Grammatically, it is the neuter plural form of the adjective ελληνικός, but very often in Greek these neuter plural forms are used like nouns to mean the Greek language, the English language, etc.

So after verbs like μιλάω:

• μιλάω ελληνικά = I speak Greek
• μιλάει αγγλικά = he/she speaks English

You do not need an article here.

Because καλύτερα is an adverb, and it modifies the verb μιλάει.

The sentence is not describing a person as better; it is describing how someone speaks.

• καλύτερος / καλύτερη / καλύτερο = better (adjective)
• καλύτερα = better / best (adverb)

So:

• μιλάει καλύτερα = speaks better

That is why the adverb καλύτερα is the correct choice.

Greek often uses a comparative + από όλους structure to express what English often says with a superlative.

So:

• καλύτερα από όλους = better than everyone
• in natural English, that usually becomes best of all or the best

This is a very common Greek pattern.

Από is the word used here for than in a comparison.

So:

• καλύτερα από όλους = better than everyone / than all

And όλους is the accusative plural masculine form of όλος (all).

It is masculine plural here because it refers to people in general. If the group were all female, you might hear:

• από όλες

So από όλους is the normal general form meaning than everyone else.

Yes. Greek word order is more flexible than English word order.

This sentence has a very natural order:

• Ποιος μιλάει ελληνικά καλύτερα από όλους;

But Greek can move parts around for emphasis, for example:

• Ποιος μιλάει καλύτερα ελληνικά από όλους;

That said, the version you were given is very normal and clear. In questions, the question word Ποιος usually comes first.

A rough pronunciation is:

PYOS mi-LAI e-li-ni-KA ka-LI-te-ra a-PO O-lous?

More approximately in IPA:

[ˈpços miˈlai eliniˈka kaˈlitera aˈpo ˈolus]

A few helpful notes:

• Ποιος sounds roughly like PYOS
• ει in μιλάει sounds like ee
• χ does not appear here, so everything is fairly straightforward
• Stress falls on:
  • Πό-
  • -λά-
  • -κά
  • -λί-
  • -πό
  • ό-

It is neutral and natural. It can be used in both everyday speech and writing.

Nothing in it is especially formal or especially casual. The only small point is that μιλάει may sound slightly fuller than μιλά, but both are perfectly normal in everyday Modern Greek.

Yes. Greek has more than one natural way to express this idea. For example:

• Ποιος μιλάει τα καλύτερα ελληνικά;
• Ποιος μιλάει ελληνικά πιο καλά από όλους;

But the original sentence:

• Ποιος μιλάει ελληνικά καλύτερα από όλους;

is completely correct and very natural.

It is a good example of how Greek often says better than everyone where English may prefer best.