What would be the best starting Kayak for me?

I live in the Ozarks and there are all kinds of rivers that range from almost non moving water, to extreme white water. I was a Kayak that will be able to handle both pretty well, and that I can learn in. My brother in Law has a Dagger (can't remember the brand) that I played around in and it seemed perfect for what I need, but is there a better Kayak out there for me to start with? I liked how the dagger had the drop down fin that I could lower to help track straight in water, he had a cheaper Kayak with him that didn't have the fin and it didn't track nearly as well. I am about 5'11 and about 140 lbs, so I'm not sure what size I would need.