Vote below.
I vote Squiffy.

Not really comparable.

Squiffy is best for CYOA type games, Quest for standard text based games.

It's like asking, which is better: apples or balloons?

Or basically do you like CYOA or standard. It is an opininon. I just like CYOA better than standard.

Quest is better...
Quest can act like Squiffy, but Squiffy cannot act like Quest...
BUT... it also comes down to if you are a programmer or a story teller...
Squiffy is better for the story teller...
Quest if better for the programmer, altho, a simple story can be told with Quest just as easy as With Squiffy...

I'd actually disagree. If you're good with Javascript you can do almost anything in Squiffy. The following is the built in Squiffy:

http://damian.me/game

Its an Unfinished development test but it shows the flexibility and power of Squiffy.

I've experimented with Quest and it's great for text adventures, but it's far harder to mod plus relies on server side components that means you can't distribute as easily.

I've actually played around using Squiffy as a foundation for a point and click adventure, complete with animation etc. It really is a very powerful tool.