My favorite capos for squarenecks are:
*Charlie’s for acoustic dobro
*Walworth for electric dobro and lapsteel

The tone on open strings with the Charlie’s is the best

The Walworth is the easiest to use, smallest, lightest, and when playing electric lap or dobro thru the Nashville pick up/JD Aura, you don’t notice any tone issues with the Walworth.

Shubb alledgedly has the best acoustic tone of all, but I could never get a good fit on my dobros.

As Brooks wrote above it's all about the fit. If you have it dialed in on your guitar, then it's the closest thing to a standard guitar capo since it clamps around the neck and with good quality flattop guitar capos it's difficult to hear what I refer to as "tone death."

I have a Shubb in a drawer that I keep saying I'll spend an afternoon trying to get dialed in, but I never seem to get around to it. 

When  the likes of Tony Rice played with a capo - you never really noticed it, because a quality clamping capo does a good job of preserving tone. 

Charlie's capo is great, and I also use a Bradley - also great . Players here and elsewhere sometimes say they hear no difference when using a Charlie's vs. no capo.

I don't buy if. Even with my aging ears I do still hear a little tone death from Charlie's. 

I have said for many years that  using a "floating" on the strings dobro capo, regardless of the brand, there is a subtle skill set to  picking  capo'd open strings  where the listener doesn't notice it. Jerry Douglas in particular is a master of the technique.

it's sort of  a "sleight of hand" thing - getting good tone on the capo'd (but open) string, and getting off it quickly - not lingering. 

With capos, tone preservation is obviously a top priority.

But there are other considerations…

How easy is it to align to fret lines?

How quickly can it be applied/removed? (critical for gigs, jams…).

One or two hands?

Does it drive certain strings sharp due to uneven tension?

Does it work for multiple resonators?

All in all, I (like many) find the Charlie’s to get the highest marks when looking at all the combined factors.

In a perfect world, an ideally fitted Shubb would provide great tone and pitch accuracy due to its inherent design. In reality, I never could get mine to work right, and certainly not with multiple instruments.

And even with the good ones like a Charlie’s, I always detect tone sacrifice on open strings. (My first test with any capo is a simple bar pull-off on 1st string…always a detectable difference to me…)

All this said, your choice between the Charlie’s and Shubb will be very specific to your ears and your judgment on all these factors (and probably more) ;)

Well I did purchase a Charlies pro Slide capo, it worked ok, but I have returned to the Shubb capo, perhaps it is a bit difficult to teach old dogs new tricks...I like the lower profile of the Shubb. I'm still working on learning how to play some basic dobro...

Cheers