As we have seen with the current NorCal wildfires, hardcopy paper storage is no guarantee of permanence. In 1989, a burglar broke into Lindsey Shere's house and stole her purse which had a three-ring binder that contained eighteen years of recipes/notes as the pastry chef at Chez Panisse. She did not have a backup.

Worse, hardcopy binders do not have robust searching/indexing tools that digital files can provide. With a digital archive, you can search for "chicken" and get every instance where that word appears. With a traditional filing system, you can't see that.

Ideally, copies of the recipes would be both digital and hardcopy and saved in multiple locations (your computer can still die or get stolen). As mentioned by Nancy, we have seen various file formats go quickly obsolete and various sites and services halt operation. Putting your recipes in HTML and saving them to GeoCities did prevent Yahoo from shutting down GeoCities and trusting the Internet Wayback Machine to archive your site isn't reliable at all.

There was an amazing recipe for New Zealand plum sauce at www.luckypeach.com. It's gone. The website closed and the content removed. So even if you find some digital content, it's best to make a digital copy.

The most logical file format to choose would be PDF (ISO 32000-2) which has been an open standard since 2008. Formerly a proprietary format created by Adobe, they made it free of charge since 1993, so it is already over twenty years old.

The HTML document format will also be a candidate to be read in twenty years. Likewise, the format is open and has already been around for over twenty years. Unfortunately, HTML is not portable and convenient (e.g., if you have photos or video attached to your HTML, they live as separate files).

Scanning old paper recipes does help with the permanence/archiving but unless OCR is used to scan the document and generate digital text, these scans will still fall short of being searchable.

Your best bet would be to scan old paper recipes, keep electronic copies on your computer, back up your computer and keep copies in some cloud storage service. That way, if your house burns down or your computer/purse is stolen, you still have records of the documents.

With the image of countless video storage and word-processing formats that have become obsolete (and sometimes unusable), your question has great foresight.
Meanwhile, here's an article from about a year ago here (Sept 2016) which culled user recommendations and came up with 3-ring binder as maybe old-fashioned but still reliable.
https://food52.com/blog/17908-the-best-recipe-organizer-is-tech-free-and-under-5
Have a look and see if you like it.
Meanwhile, maybe readers have more to say since then...