My immediate guess would be Hebrew due to its lack of day-to-day use in the intermediate time (maybe leading to less linguistic drift?), But what about Arabic? Farsi? Mandarin? Hindi? Greek?
Bonus question: what language is mutually intelligible with its past counterpart the farthest back that we know of?
More can be said about how certain specific languages have changed over the last 2000 years, if anyone wishes to add something new. But broadly speaking, we do have a section of the FAQ dedicated to the question of "How far back in time could I go and still communicate in [insert language]?"
For Hebrew: here is an answer about the similarity between modern and ancient Hebrew by u/gingerkid1234
This thread has some interesting answers about how Hebrew was revived as a vernacular language by u/ghostofherzl and u/gingerkid1234