Deanna's too beautiful to tell your most embarassing moments and deepest fears to, as you can't help but want to impress her and get with her. Showing all of that cleavage and wearing such tight leggings makes it very hard to confide anything to her, except your phone and room number. The last thing you want her knowing is that you've developed an irrational fear of the elastic in your underwear. Guinan's homeliness makes it so much easier to approach her with such insecurities. If her opinion of you suffers, well ... you know ... so what, then? Really. You feel you can trust her because, at the end of the day, you don't really care what she thinks ... you just know you can trust her. And that's what it all comes down to, I think.