Both have their place, but I've learned they scratch different itches. With standalones, I get that clean ending - you know exactly what you're signing up for, and there's a satisfaction to closing the book and moving on. With series, yeah, you get attached to characters, but you also risk that frustration of waiting or, like you said, feeling trapped in something that stopped working for you three books ago.
Here's what actually changed how I approach this: I started checking the publication dates before I commit. If the series is already finished or the author has a solid track record of releasing regularly, I'll jump in. But if there's a gap of years between the last book and the next one, I deliberately wait until book three or four is out before starting. Saves you from that limbo feeling where you're invested but stuck. For me, that's way better than white-knuckling through a book you've lost interest in just to see where things go.
The guilt thing everyone mentions is real though - you don't owe completion to anything. But honestly, the bigger win is making the choice upfront. Pick a series that's got momentum already built, or grab a standalone when you want to feel that sense of closure without the wait hanging over you. It's not about being a "series person" or a "standalone person" - it's about matching the format to where you're at right now.