Velvia 50 delivers for fall (autumn to us here in Australia!) richness of palette but requires knowledge of its specific lighting: it is a bloody awful film to use in bright sun. Also, in 35mm format, the tonal range is compressed which means it requires considered metering and, very often, gentle over-exposure to avoid blocking (e.g. EI40). I have used it for 20 years in 35mm with excellent results (printed to Ilfochrome Classic media) but find the results are greatly better in MF. It is easier to expose with a manual meter (spot metering especially).

Provia 100 for lower contrast but at the same time less of a Vaudeville palette. I don't think it's very punchy for fall colours. By the same token, C41 is pale in comparison to Velvia. But it's all a matter of personal taste and what you will be doing with the end result. For me, it is printing, framing and exhibiting.