I've tried both. Slimv was always very buggy for me, especially the REPL buffer. I think this was because it was made long before any of the new Vim async stuff existed, and so had to do a lot of ugly hacks to get a reasonable REPL.
Vlime was made after Neovim gave Vim a kick in the ass to add async, and it takes advantage of all of it. This lets its implementation be a lot cleaner and more stable, at least from what I've experienced.
One thing I do that makes the REPL a lot nicer: I run the actual SBCL process inside a Neovim terminal split (with rlwrap). This gives me an actual REPL like you would expect, not just Vlime's "REPL" (which is essentially two separate buffers, one for input and one for output).
I've been using slimv for hobby hacking for a while, but not professionally so you can take my commentary with a big grain of salt. You should try both, and if 'stevelosh likes vlime better you might start with that.
I like slimv a lot better myself, and prior to that I made due with a gnu screen split-window terminal with a vim plugin that would send stuff from one screen panel to the other (used that for Python, Clojure, and Node sometimes too). I tried using vlime somewhat recently, but it just felt off, hard to express everything I didn't like but maybe the experience of having to launch your REPL separately was the beginning (slimv just finds your lisp on the path). You're encouraged to compile whole files at once rather than bit by bit (perhaps sensible for Real Work), the REPL buffer is read-only which is quite bizarre to me, and the default key bindings make less sense. Feature-wise it seemed comparable since they both use Swank. The tutorial at https://kovisoft.bitbucket.io/tutorial.html which follows a classic SLIME demo vid is nicer than the vim-tutor for vlime.
> the REPL buffer is read-only which is quite bizarre to me
The way I work around this is to run the SBCL process inside a Neovim terminal split (with rlwrap). That way I get a vanilla SBCL REPL plus the stability of Vlime.
Anyone has tried both Slimv and Vlime for Vim? What are the differences? Which one gives an experience closer to that of SLIME?