Many thanks ! Now, I notice you've used the copula here, instead of tá. Would that be an instance of 'emotional estimation' as Ó Siadhail puts it, as in 'Is deas í do léine'? ' 'An-scríbhneoir ba ea í.'? Or is there another rule that you always use the copula with a comparison?
I didn't use the copula - I quoted an entry from the NEID that does what I said you shouldn't do, translating an English idiom directly into Irish.
But the reason for using the copula is because "best" is really being used as a noun in "you are the best" or "it's not the best" - it's standing in for whatever noun the definite article is there for.
"níos" is pronounced as a single syllable like "niece" in Ulster and Connacht:
Even in Munster, the second syllable can disappear in a phrase like "níos lú", giving the "neeslu" sound that you hear in this exercise: