They both can be, but Hamas is a terrorist organization that has committed terrorist attacks.

Yeah, according to the US and Israel—which, I cannot stress enough, are terrorist states—Hamas is a terrorist organization, but that does not make it so. Western governments and Western corporate media can designate anyone to be anything, but that doesn’t make it so. They are not the arbiters of truth, they are propagandists for empire.

Palestinian right of armed resistance

[UN] General Assembly resolution A/RES/38/17 (22/11/1983) stated that it "Reaffirms the legitimacy of the struggle of peoples for their independence, territorial integrity, national unity and liberation from colonial domination, apartheid and foreign occupation by all available means, including armed struggle".

Furthermore, As an Occupier, Israel Has No Right to ‘Self-Defense’.