WR250R is a 60 MPG dual sport bike with DOT tires, 10,000 RPM fuel injected motor, and 3,000 mile oil change intervals.
WR250F is a dirt bike that can be plated in some states. It's lighter eight and more powerful than the WR250R, but has much shorter maintenance intervals.
In case it's not clear to you already these bikes are similar in name and color only. Their frame, engine, transmission, and suspensions are quite different from each other.
From your description of how you intend to ride I think the WR250R is the easy choice.