The question seems to be more about infrastructure than the products themselves. In reality, this will mostly diverge the moment it's handed off to your ISP of choice.
Today, both are deploying GPON-based products, aiming for 1:32 splits (from what I have seen though, CityFibre rarely gets close to 1:32). The products sold on CF allow for symmetrical up to a gigabit. Whereas Openreach currently caps at 220 up.
In the future though, things look a tad different. CityFibre has already signed agreements with Nokia to deploy XGS-PON from April (when you can get on their new XGS-PON network is another question), and as far as I am aware there's no news on future tech from Openreach.
Openreach are currently (or about to?) trial 1.2 and 1.8 Gbps down products, again, based on their existing GPON infrastructure and limited to 110 up. CityFibre has no public announcements of products that exceed their symmetrical gigabit service.
tl;dr, it's mostly the same today, CityFibre offers faster upload products. You'll want to look into your ISP options because the differences will exist there. CityFibre's longer-term plan is much clearer.