Seconded here. So far only used ready made sets, especially the fantastic CCNA one from Jeremy's IT Labs. But I guess that if I fix few more errors, I'll break into creating my own cards.

Creating a card is a first step in learning that card. Worth it! And you don't have to do that on your phone - there's a desktop app available.

I found that creating and adding to my own decks is the best way to learn. It's also a lot of fun creating the cards/notes structure, with some cards being created conditionally upon state of certain fields in the note, etc. It's a bit like creating a database schema.