I can recommend Velvia 100 (without F) and Provia 400X from personal experience. If you intend to shoot autumnal trees, Velvia 100 is hard to beat. Provia 400X has a very rich but more natural saturation than Velvia. I like it for its sharpness and the speed. Grain is a bit more of an issue, though it is comparably fine for an 400 ISO slide film from what I´ve read (Have not tried any other).