Belladonna for her patented slide into throat, smile, open mouth while putting pressure on the tip and wiggling so that you hear that satisfying wet 'clack'. Plus she's the closest thing porn has to royalty, so that's another plus in her favour.
On this list, Annette Schwarz. Don't like the sound of her voice, but the girl is a born sword-swallower. Never seen her come across anything she couldn't fit down her throat.
EDIT: That's odd. How come Belladonna's name produce an automatic link to her Freeones profile?