Is ancient Greek similar to Latin?
Ancient Greek and Latin were broadly similar in structure, but have a limited overlap in vocabulary, apart from various loan words. Both languages are highly inflected. Nouns change their form according to how they're used in the sentence.
What is better ancient Greek or Latin?
Learning Latin is (generally speaking*) easier than Greek; you don't need to learn a new alphabet, and if you know a little bit of Italian, French or Spanish, you might recognize some of the words. Even English has, because of the large influence of French, many words whose roots can be traced back to Latin.