There is no good and evil, only perspectives.
Mahishasura is probably the first (and only one) name that comes to mind when one speaks of Devi Durga. Mahisha was an Asura.
Asura is typically construed as evil, and is used interchangeably with Danavas, Daityas and Rākshasās, mainly because in English, they are all demons! But all asuras were not considered evil. In fact, King Mahabali (who was an Asura) is still worshipped in India – the festival of Onam is in his honor. Here are some of the niruktas (etymologies) of the root word asu.
Asu can mean, prana – life breath, life- force; in this sense, asura means ‘one who brings, gives prana’ (asun, pranan rati, dadati iti asurah).
Asu can mean, kshepana – to throw, throw about, scatter, remove away; in this sense, asura can mean ‘one who removes undesirable things and dangers’ (anishtakshepanasheelah); by the same sense it can also mean ‘time’, since ‘time moves or scatters everything (asyati, kshipati sarvamityasurah – kaalatmaa samvatsarah)’.
Asu can mean, prajna – awareness, wisdom; thus, asura can mean, ‘one who is endowed with wisdom or awareness’.
Asu can mean, bala – strength, force; thus, asura can mean ‘one who is endowed with a great strength’.
Likewise, asura has been used to connote ‘someone who is very charitable’; at some places asura is used to mean, megha- clouds.
Asu also can mean food, water and wealth, and the word asura attains various meanings in accordance with those connotations to denote, ‘one who possesses food’ etc.
The word asura referred to both inner tendencies, as well as clans. Bhakt Prahlad was born into the asura clan of Hiranyakashyapu, but he wasn’t evil.
अस्यति देवान् क्षिपति इति असुर: – the ones who oppose suras or devas, are asuras.
Food for thought!