I'm firmly in the "finish the story" camp.
Whenever I get to the end of a book that has a cliffhanger before the main plotline is resolved, I feel cheated. It doesn't make me want to read book two, it makes me want to avoid everything that author writes in future, because I know I'll be similarly short-changed again. I don't want to pay for half a story, I want a beginning, a middle and an ending, and if a series keeps ending on cliffhangers, I'll immediately suspect that the author has no idea how to write endings.
It seems to be a trend with particularly self-published series, that plotting takes inspiration from TV series arcs. What these writers don't seem to realise is that the better way to do that is to make "book one" equate to "season one", rather than "episode one". A full arc that wraps up at the end (with the assumption of cancellation), but leaves enough threads dangling to pick up in season two - rather than an exciting introduction to the characters, and then "stay tuned next week!" to see how their problem is resolved.