This is the key point for me:
org-mode has a lot of capability and is really flexible for changing or moving content
Texinfo is great for static manuals, and has nice features for navigation, tables of contents, indexes and bookmarking. But it is a "compiled" language, meaning you write in
.texinfo format, and then compile to
.info files that are then installed in
dir files before you can read them. Consequently, you write in one file, and read in another, with a processing step in between.
Org files, on the other hand, are read-write. You read and write to the same file, with no processing. For anything that you will regularly modify and update, this is going to be much easier to manage than texinfo. The main features missing from org mode are menus and indexes. You can get some of those features back with links, but it won't be quite as powerful or automated as texinfo.
So, if you're writing yourself lengthy and detailed (i.e., complex enough you want tables of contents and indexes) reference material that you don't need to modify much, texinfo might be nice. But if you are frequently adding notes to these references, org mode will be much easier.
(Another nice thing about org-mode is that you can link to any other file or webpage. I'm not sure if texinfo does that?)