I would like the bike as a bit of a car replacement for journeys around home so a bit of speed may be helpful but they all look pretty quick to me
There are many differences between electric-assist bikes but before you get carried away by any advertising, forum advice or any other reason, there are certain fundamentals you need to understand.
1) Before any other consideration, set a maximum budget. I say that because it's easy to simply assume that you get what you pay for therefore dearer must be better. That's not true and a £2600 bike is not £2000 better than a £600 bike. Some very capable bikes can be had for nearer that lower figure.
Provided you only consider legally-compliant bikes and contrary to what I said in the opening sentence, there isn't really all that much of a difference in performance, particularly when you consider that they all cease to provide assistance around 15mph. Some are better hill-climbers than others but very few current machines are useless in that regard.
2) Bicycle weight: Think around (or less than) 20-23Kgs for a bike and ignore anything much over 25Kgs although there are a few, very few, exceptions. Light weight is a major plus on an EAPC.
3) Dealer proximity and support: Unless you are well versed in electronics and have experience in stripping bicycles to bits, the help of someone with intimate knowledge of your chosen steed is essential. If you have a dealer nearby who has been in business for a long time, with proper premises, then you could probably be a little flexible in points (1) and (2) above but with this caveat:
4) If you live in a house with no stairs to carry the bike up and you will never want to carry it on or in your car, the weight is of less importance. If, on the other hand, you might want to attach the machine to your car as so many regular cyclists do, then weight is of paramount importance. Although a tow bar and/or trailer can be utilised if you have a heavy bike, unless you already have one of those, it represents further additional expense.
Have fun discovering the world of EAPCs.
Tom