Phew! That was a long and pretty comprehensive write up! Good on ya there~!
And even for Renegade's beloved "YouTube Downloader and Converter", you'll need to write a many-mouseclicks (!) macro in order to put the download on a single key, i.e. these developers are unable even to implement some little keyboard shortcuts, which would be a strict minimum for 30-bucks-a-year sw imo. Sorry, I always get harsh in the end for being overwhelmed by dissatisfaction, but I simply don't understand this blatant, ubiquitous lack of understanding of users' even most basic needs, all sorts of free and paid sw combined, with rare exceptions.
I'm not tied to any specific piece of software, except through experience, and I've just never had many real problems with YTD there.
Now, to be fair to the authors of this kind of software, they have a tough job. I'd like to outline just a bit of what they face...
The generic term for this kind of software is a "scraper". All scraper software suffers from the problem of web sites updating their code and then the scraper breaking. This requires vigilance and work to keep things smooth. i.e. The software *WILL* break. That's a given. (I've written this kind of software before many, many times.)
So, you're stuck with having to get users to update the software. This is a real pain for the users, but believe me... it's a MUCH greater pain for the developer/author. I'll skip the nastiness there - but you can probably imagine the horrible nastiness associated with updating - I've been called names and accused of malicious intent simply for talking about having an automatic updating mechanism that lets users choose if they want to update... There is simply NO pleasing some people.
For YTD, I've simply kept it up to date. I had one short period where they couldn't update it quickly enough, but I've got the current version, and it's working fine for what I need - e.g. downloading videos and playlists and converting, etc. This will happen with all scraper software.
For global shortcut keys, that's an entirely different can of worms. Suffice it to say that you need to be judicious with them, and that browser integration isn't all that simple when you do client software (tonnes of issues there - I'll skip them here).
But I'm not sure I read which you'd decided upon. Please to post your final decision as I'd like to try that out. It seems like you've more than done your homework, so I'd like to take advantage of your experience there from the purely user-perspective.
Again, thanks for posting all that info there!