Smooth Knob Tailed gecko or...

[mathaldo]

A crested gecko.

I'm going to be getting a 20 gallon in the next month or so, and I am looking to get 1 or 2 new geckos. I'm really really interested in 2 very different ones. Crested geckos, and knob tailed geckos.
Now I have a few questions about them.
Which is easier to take care of?
Can I use sand for a knob tail, instead of paper towel?
Do either need a fluorescent light fixture?
Can a pair of either speices live comfortably in a 20 gallon?
Are either easily stressed with human contact? As in noise, handling, etc.
I may post some more questions later, but these are the only ones I can think of now.
Thanks,
Mat