This is always a difficult choice.
Do you go for words that will enhance the story but will alienate readers opinions or do you just thick "fuck it" and go for the best storyline you can. Usually I let the story dictate which word I use. Here are a couple of my favourites: backdoor, arse, arsehole, butt hole, puckered little star, anal chasm, bowels, rectum, bum, bum hole.
I have used more extreme names but like "Hotghirl" above, I didn't like it but it seemed appropriate to the story.
Not in any particular order of preference and maybe not the best but certainly my favourites.
Dave Gilmour (Pink Floyd)
Brian May (Queen)
Jimmy Page (Led Zeppelin)
Richard Z. Kruspe (Rammstein)
Billie Joe Armstrong (Green Day)
Jeff Healey (Jeff Healey Band)
Lindsey Buckingham (Fleetwood Mac)
George Harrison (Beatles, Travelling Wilburys)
Gary Moore (Thin Lizzy)
James Dean Bradfield (Manic Street Preacher)
Happy birthday Dancing Doll
Without doubt a real flesh and blood cock
No preference. When my partner turns me on that much I'll beg him to fill me up and I don't mind where he uses it.