Anyway, I don't know much about all these - and since Avi and others have been putting work into Scriptaculous that is probably what I will go with.
Well, I don't know much about the internals of all these JavaScript frameworks, however I think Avi choose Scriptaculous because it has a consistent object interface that can be nicely interfaced with Smalltalk. By using the Scriptaculous Seaside library you don't need to write a single line of JavaScript, and that is certainly a big advantage.
Mewa or Magritte might be interesting for you too, if you plan to do a lot with forms and dialogs. Both frameworks help to build and validate forms automatically. Since Magritte is described with its own meta-framework, it is even possible to let the users customize and build their own forms from the web.
In fact - this is exactly what we want to be able to do among other things. Or at least have forms dynamically built from a model of "Form" and "Field" objects.
* Adrian Lienhard, "Mewa: Meta-level Architecture for Generic Web-Application Construction," Technical Report, University of Bern, November 2003, Informatikprojekt (http://www.iam.unibe.ch/~scg/Archive/Projects/Lien03a.pdf)
* Stéphane Ducasse, Lukas Renggli and Roel Wuyts, "SmallWiki — A Meta-Described Collaborative Content Management System," International Symposium on Wikis (WikiSym'05), ACM Computer Society, 2005, To appear.
The second paper has got a chapter on Magritte, despite very few class comments this is the only written documentation right now. Unfortunately I cannot give you a link to the paper as it wasn't published yet, but I will send a copy to your personal e-mail. And there is hope for more documentation, I am currently writing a paper covering Magritte in deep ... Magritte is available on SqueakMap, the package automatically pulls in everything it needs.
Cheers, Lukas
-- Lukas Renggli http://www.lukas-renggli.ch