The answer is "all of them!" ESR wrote "Every good work of software starts by scratching a developer's personal itch." You'll be much more effective working on a program that you use and want to make better, compared to a beginner-friendly project that you have no interest in. Instead of looking externally for projects, look inwards. Think about the software you already use, and how it could be better: that stupid an…
This is seriously not true. I've had experiences of projects I tried to get involved because I liked the software but where the maintainer had zero interest in involving any new people. It's lovely that developers scratch itches and create cool software - there isn't anything that implies those same people want to work with other new people. I'm glad you had a good experience and maybe I was unlucky or whatever but I…
That's absolutely true, but, given that this is open-source, there's always the option of maintaining it yourself. Of course, for someone who's an absolute newcomer, it's better with a buddy.
Tell you what. I'm interested in projects in C or Python doing systems-y things and that can be compiled on Debian (think stuff in the space of GLib, NetworkManager, apt... but also anything tinier, obviously). If you find a maintainer who's wholly uninterested in adding people, you've got a new feature you want, and you want someone to work with, shoot me an email, I'll probably be up for helping out with it.
Chances are that the maintainer will be interested in the feature, just not in mentorship. And even if the maintainer is just antisocial, chances are maintainership will change, or the world at large will benefit from a fork, or the Linux distros will be willing to take your patches even if the original maintainer isn't.