Depends on what you want. I have a few authors like Brandon Sanderson, Joe Abercrombie etc. Some comics like XKCD, Sword Comics etc. Some work / programming related ones, news / blogs of lots of applications / software I use, some other hobbies related ones like gaming etc.
I'll recommend starting from a few and then slowly growing it. I used to have tons of feeds, and would have 100+ new items every day, some time even more than 2 or 300, which became unmanageable, so have removed lots of stuff I didn't care about too much. You can of course just add everything you want, and then slowly remove stuff that you think isn't too important.