Today's writers are emulating a old sales techniques used by Charles Dickens: the serial. While I have my personal preferences regarding serials, I have to say that I appreciate when the author notes in the book summary whether the book is part of a series or a serial. Don't know the difference? Here's a quick description:
Since I enjoy reading book reviews, I can tell that there are many readers who detest serials and will leave negative feedback and cliffhanger warnings. I don't particularly like serials and will thank a reviewer for leaving a cliffhanger warning if the author doesn't explicitly state in the book blurb that the book I'm considering purchasing is merely an installment in a serial. More often than not, I will decide not to purchase the book.
Back in the '80s and '90s, I bought series that, in all honesty, were serials: The Belgariad, the Mallorean, Thomas Covenant the Unbeliever, the Shannara series, etc. However, when I started them, I knew they were going to continue over multiple volumes. It was difficult--and can still be--to find a standalone fantasy novel. With the advent of indie publishing, there are more standalone novels than ever--and more serials.
So, what's better? It's purely a matter of preference. There's no right or wrong. To other writers, however, I ask you to please, please, please specify clearly if your book is part of a series or a serial. That courtesy annoys far fewer readers than not doing so.