Series? Or Stand-alone books?Well, it really depends on the book. I feel like every book being published nowadays is part of a series which gets really irritating when it doesn't need to be. A lot of the times, a series will just drag on where it could have fitted much better into a single book. I also feel as if random problems are casually thrown in just so an excuse for another book can be made.
On the other hand, I love a lot of series and sometimes, they need to be series. Like, can you imagine if Harry Potter had been just the one book? It still would have been great but it works a million times better as a seven-part series.
I think that most of the time, I prefer series because we get to learn more about the characters, setting, theme, whatever. Plus, if I like the book/writing/author, I get more to read!
The Final Verdict: Even though a series can be completely unnecessary sometimes, I generally prefer it to a stand-alone book.