In Italian the word amara means bitter. It is used as an actual word, together with the masculine form amaro. So if you will ever move to Italy (which I will in the future) it just isn't usable at all.
Mara means bitter too but it is at least not a common word meaning bitter, as far as I know. I prefer the sound of
Amara. Ahhh this is too difficult. If I hadn't lived in Italy for so long and would never live there again definitely
Amara. For someone else without plans to go to Italy also
Amara. Otherwise
Mara, I guess.