Note, [i:] as in see, and [ai] as in high. /I/ is not an option:
[ni:] => neither
[nai] => neither
In most of the United States, the [ni:] pronunciation (e.g., [ni:], as in "knee") is far and away the most frequent and has been from this country's birth. It was not until the 19th century that the [nai] pronunciation [e.g., [nai] as in "nigh") was borrowed from British speech, and compilers of early American dictionaries (e.g., John Walker, 1836; Noah Webster, 1838) did not show the [ai] option at all. In 1911, the Century Dictionary added [ai] and from the 1930s on, [ni:], [nai] has been the pattern in American dictionaries.