Actually, going by documentation alone, one would think that angels are rarely feminine. The story of the Flood is, to start, is rather disjointed--it isn't clear if the wickedness God sought to cure was due to the 'sons of God' (angels) taking wives, or if that's just additional knowledge for the story. Either way, it's our first indication of angels being male. There are more indications, both in the Bible and Apocrypha of angels being male, with the only female indication I'm aware of being Zachariah 5:9-11, verses describing two women with wind in their wings.

Much of what we know, or think we know, about angels comes from various imaginations or interpretations. For instance, those who choose to believe that angels are sexless quote Jesus' explaination of there being no marriage in heaven--we'd be "like the angels". They ignore both the facts that sex/gender is mentioned elsewhere and that he says no marriage, not no gender.

I'm not sure where the various New Age images of pretty female gardian angels comes from--I doubt it stems from the passage in Zachariah. More likely, people just like imagining them that way and the image has spread.