grammar - Should the word A or An be used for this statement?

I am trying to create a letter and before hand I need to know rather or not to use a or an for a specific sentence. I know that U is a vowel, but because of the way the sentence sounds I re-framed from using an and used a.

while also ensuring a unique style.

Should I use the statement above or should I use this:

while also ensuring an unique style.

Answer

Using indefinite articles (a, an) in English depends on the sound that begins the next word:

Nouns beginning with a consonant: a boy, a user (sounds like 'yoo-zer, begins with a consonant 'y' sound, so 'a' is used), a university (again starts with the consonant 'y'), a unique (starts with the consonant 'y'), a European girl (sounds like 'yoo', starts with the consonant 'y')

Nouns beginning with a vowel: an egg, an ultra (sounds like 'ol-tra' and starts with the sound/vowel 'o'), etc.

Quick note: the vowel [u] doesn't have anything to do with the letter 'U'.