I think that after London region then Liverpool region is the second best thing overall.Southampton is best for any southern-england based polity, bristol/kingston upon hull/liverpool is best for a celtic england, york is best for a north sea empire, but london is best overall.
- It is more central among the British and Irish isles
- Has god river connectiond with inland England
- Has a protected harbor
- Would likely boost anglicisation of Wales
- Could strengthen Englands infuence in Ireland, perhaps lead to colonisation of Ireland
Still this ATL capital would get less trade than London as capital did OTL.