Though Lopen is certainly up there (and I mention this for no reason at all), he isn't the top of that mighty heap. He is one of two characters (Rosharans) whose dialogue I enjoy reading outloud. Jasnah is up there too, as the blood of the skeptic runs(albeit coldly) through my veins. I have high hopes for the Herald Taln (or whatever variation) as he is hands down the most badass character in the series (Stormlight is my favorite and default series to be discussing) for his incredible feat in not breaking under torture for thousands of years and upon finally breaking and finding himself back on Roshar is THRILLED TO FIND OUT HOW LONG HE WAS TORTURED FOR, just for how much time he bought people. But it is Dalinar who I most connect with, as we share similar emotional makeups. There's few characters I don't enjoy in some way though.
As for book, I'd say it's a forthcoming Stormlight Archives Omnibus.