Personaly i found abcl a bad experience.
Thoughts on ecl & clisp ?
sbcl works nice & fine. But i’t’s the only lisp implementation i know.
There are good books on racket-scheme & chez-cheme.
The only book i know for lisp is, “Common lisp , a gentle introduction to symbolic computing”.
If I were a paying Franz customer and I would be interested in SLIME/SLY improvements, I would kindly ask them to provide it. Maybe they would then just do it or ask the customer to pay for it. That’s what technical support is for.
Second: as a Franz customer one could get the source code for much of the product. I’m not a customer, but I guess this possibility still exists.
I think it can actually be the opposite. Among new Lisp users GNU Emacs is often cited as a hurdle.
Allegro CL comes with an GUI based IDE on Linux, Windows, and Web browsers. This makes it possible to use it without GNU Emacs + SLIME/SLY. I consider that to be a feature. The IDE of Allegro CL has a bunch of features: https://franz.com/support/documentation/10.1/doc/cgide.htm#menus-dialogs-1
Best: the stuff is written all in Allegro CL itself and can be reused.
Oh wait, it really ships with a GUI-based IDE… I’m convinced—Allegro is good, especially when paid. When talking about free version, my non-introspection comments still apply, but they are kind of implied for a free version of proprietary product.