Electric Bike - what to look for

I’m looking to get an electric bike for daily commuting Bristol - Bath. 16 miles with a big hill either end. Want to try and make the cycle in about an hour without breaking a sweat - I realise speed is capped at 15.5 on legal bikes. Aiming to spend £2500-£3500 using cycle scheme.

What are the key specs to look for? Is Bosch/shimano/ any other a better motor? Does integrated vs non integrated battery matter? Are particular gears or brakes better on an ebike? And does any bike manufacturer have a better reputation than any other?

Thanks UKBikers!