Both 🙂
Standalones …
When I read a good standalone novel, then I finish it and want to know more about those characters. I want there to be a sequel, and there isn’t. When I read a good standalone novel, I’ll generally read the next book from that author but might be a little disappointed it’s not a sequel, or it’s not as good as the previous novel.
Series …
When I read a good novel that’s part of a series, then I finish it and (wait for it!) want to know more about the characters. So I’m always pleased to know there is already a sequel available, or that a sequel is planned (even if I have to wait for it). It’s something I’ll watch out for and sign up to review, or buy on preorder. Because I really want to read that book.
When I read a less-good novel that’s a standalone, that doesn’t usually affect whether I want to read their next book. But when I read a less-good novel that’s the first book in a series, l’ll usually sit out the rest of the series. And then the author might fall off my radar, and I might not read the next series either …
So while I enjoy standalone novels, I much prefer reading a series I enjoy. But I’ll rather have a standalone than a series I don’t enjoy.
Like you, I have to say yes to both. I often find standalone novels to have a better structure and to be better written. Even for those series in which the books can be read apart from the others, there seems to be something “missing”. But I guess that’s the point to get the reader to buy the next book.
That’s a good point – a good series book will set up the next story, but that inevitably leaves you with that “missing” feeling.