Personally I'd suggest the Bronica ETRSI. It's got the best combination of features and prices from what I've seen.
Second choice would be the early Pentax 645. Problem is you'll be paying more for a camera that is older.
Doing nature you can get the Bronica with a waist level finder and the 75mm lens to start. The 40mm and 50mm older model lenses aren't that expensive used. Some of the features with the Bronica might not be of interest to you. Leaf shutters. Removable backs.
The Pentax adds a built in meter and motordrive. Both things you could add to the Bronica but from the sound of it neither are things you'd want to. Pentax lenses tend to be more expensive then Bronica lenses.
Scroll down and they offer a feature comparison of the different cameras. They all offer something different.