If you are going from one Openreach FTTP provider to another, the fibre bit wont change, its how your connection is routed from the exchange onwards that will be different. Like any ISP change really, it depends how the bit from the exchange to the ISP is handled and how good the ISP itself is.
However, Vodafone might be CityFibre if they are available in your area, which would mean installing a new fibre to your property and a completely different network.
If its CityFibre, your upload should be the same speed as your download, which I'd argue is better.