That's like asking whether to buy a Canon or Nikon camera. In the end it's entirely your decision. What feels and looks the best for your specific use. You need to visit local ebike stores, ask questions and try out a couple different models. Then think it over for a week before buying. Even then you could buy on impulse that you might later regret ... haste makes waste or it may be a perfect marriage ... Good Luck!
Deciding what kind of ebike to buy can be as challenging, if not more, as deciding what kind of car to buy. Your best bet is go to an ebike store(s) and tell them you aren't sure what would be the best ebike for your use.Find a reputable store where you can actually try out a couple types. Then go back home and sleep on it a week before deciding what kind of ebike to finally purchase (don't let them sucker you into an impulse buy before you leave their store.
Consider the proprietary construction and availability of spares. I've heard horror stories about service.
Also, DIY.
Would like to see photos of your trike.
I think the German made bikes have been designed to get the most out of 250W. No Chinese parts. The Brose motor produces 90nm with a 250W rated motor, so hard to replicate with DIY parts and still be within the regulations.
"Germany has strict laws and regulations for e-bikes, including:
Age: Riders must be at least 15 years old.
Motor assistance: Motor assistance is only available when the rider is pedaling.
Speed: The maximum speed is 25 km/h.
Headlights: All e-bikes must have a non-flashing white or amber headlight.
Brakes: All e-bikes must have two separate brakes.
Weight: The e-bike must not weigh more than 55 kg.
Riding restrictions: E-bikes are not allowed on all routes, including moped paths, tourist routes, and scenic routes. They are also not allowed to ride in contraflow on one-way streets, except where permitted by traffic signs.
Traffic rules: Cyclists must follow the same traffic rules as drivers, including stopping at red lights. At junctions without traffic lights or right of way signs, the right of way goes to the vehicle on the right.
Insurance: S-pedelecs require insurance and an insurance license plate.