"These are the sandwiches whose tomato is good."

Translation: Αυτά είναι τα σάντουιτς των οποίων η τομάτα είναι ωραία.

[Dmatafonov]

αυτα τα σαντουιτς, αλλα αυτες τις γεναικες - when should I use αυτα and when αυτες? What is the rule?

[troll1995]

Αυτά->neuter nouns plural, αυτές->feminine noun plural, ;)

[mizinamo]

And αυτοί (nominative) / αυτούς (accusative) for masculine plural :)