Book to series lets you stuff in a little more of the detail and run at a slightly more relaxed pace of plot, so it makes sense that having more runtime usually turns things out better. Not always, but usually. Movie pacing goes a lot faster and sacrifices more than a few things. I remember being extremely miffed at Potter movie #4, I think, because they made that movie without a subplot that comes back in a later book and is plot-important at that point. And it really doesn't go great with books that stay a lot in a character's head, so Hunger Games adaptation was really focused on "Arena! Battle! Kids killing kids!" da then "Hero of the rebellion!" but it couldn't really do the work of showing us how Katniss is suffering from all the things she didn't want and all the people who want to manipulate her into doing what they want. We didn't get a whole lot of "Katniss understands Snow is going to die, but had also figured out that Coin is only going to institute more of the same, so her best shot at breaking the cycle is to kill Coin and let Snow die and hope something better happens in the chaos that ensues."

So, yes, give me mini-series over movies every time.