On top of her other awesome attributes (that would be spoilerish)
I just started using her as a companion and while doing her personal quest started sneaking. 
Upon entering into sneak mode:

Cass - "Shhh... we're hunting shitheads."
 
I laughted my ass off!
That's it, now I can't use any other companins, too much awesome.

Yeah, but carrying whiskey is kind of a pain in the ass! imo.

She put on the power armor I didn't want. Too bad, I liked her hat.

I'm a fan of Arcade. 
 
"If you want me to die quickly this is clearly the best tactical choice"

Boone is a beast

I typically stick with Boone because he is so powerful, but Cass is definitely my favorite companion.

I kinda like Veronica as I got a mod to make her look like Felicia Day, her voice actress. Other than her, Boone is quite the handyman especially when I'm playing an unoffensive character (i.e. only putting points into speech, lockpick, science, etc.).

I took Cass to the Van Graffs and had her murdered . My boy is Boone. I love just walking through the wastes and seeing some fools head pop off from out of nowhere.

my opinion of veronica is much higher now that she has a ballistic fist that she's been punch-shooting dudes with one hit kills.

" my opinion of veronica is much higher now that she has a ballistic fist that she's been punch-shooting dudes with one hit kills. "

I had her for awhile. Then she started limping around and kept asking for whiskey. So I had to put her down like a horse. It's unfortunate for me because she came back to life. So we parted ways. 
 
Now I have Boone and the dude is bad ass. Now, every once in awhile, there's a glitch where I keep hearing Cass asking for Whiskey. Every time I hear it, it puts me on a bad guilt trip.

Cass is only good up close and behind.

I had Boone and Cass for a while until I completed their quests. Since then, it's been all Veronica. She has a Brotherhood suit of power armor and a unique super sledge. She's pretty much the melee version of Boone.
 
Also, Felicia Day.

What's Cass' ability? Ranged?  
 
Also how many companions can you have, right now I have the floating robot equipped with a laser rifle, and Boone. Nothing gets close to me :P

" What's Cass' ability? Ranged?   Also how many companions can you have, right now I have the floating robot equipped with a laser rifle, and Boone. Nothing gets close to me :P "

I'm sorry, OP.  You misspelled "Boone" in your title.

Cass has the best lines. I guess if you want the game to play itself, put Boone in the party and hide behind a rock while he cleans up.

" Boone is a beast "

Using Boone and Rex right now. ED-E quest bugged for me

Cass is awesome.  Just ask her opinion about the NCR.  You'll be glad you did.

" @jams: At the bar in the mojave outpost.  I agree, i think Cass has the best personality of the companions, but I switched her out to use Boone since hes so much more powerful.  Boone is kind of a dick though. "

I beg to differ:  

" HK-47 begs to differ, fleshbag. "

" @SuperfluousMoniker said:

" HK-47 begs to differ, fleshbag. "

You sir, are full of win! "