I tend towards using neesh for the adjective and nitch for the noun. Though, when reading, I always see neesh, as nitch makes no sense since the word ends in an e, not an h, and there is no t, which seems to be required in English.
And of course you say year-ro. Where in the world can you say it wrong and not be immediately thought of as a dunce?
Just don’t say either word with an affected accent or make a big deal out of your pronunciation, and it won’t sound pretentious. In a casual American accent, they sound fine.