Well, every subreddit is an RSS feed (ex: http://reddit.com/r/artificial/.rss) so if you have a favorite sub or two, you can follow those in an RSS reader.

Likewise, there is the HN RSS feed: http://news.ycombinator.com/bigrss

Also, all arXiv categories have RSS feeds associated with them: https://rss.arxiv.org/rss/cs

and you can also do individual subject classes within a topic:

https://rss.arxiv.org/rss/cs.LG

But of course if you're asking about my favorite feeds, I guess I'd have to say "my own". :-)

http://philliprhodes.name/roller/blog/feed/entries/atom

https://www.fogbeam.com/blog/fogbeam/feed/entries/atom

Arguably the #Junited2005 thing this month has been about finding good blogs etc; most seem to have RSS.

Eg see: https://mastodon.social/tags/Junited2025

My most reliable way to find feeds is to read things here. Then if I like the article I subscribe to the blog.