My pick was the Brose mid-drive motor available in Tour 50nm/City 75nm/MTB 90nm models. I then bought an ex-demo one off model from a localish bike shop. https://www.ebike-manufaktur.com/en/e-bikes/11lf-shimano-deo...
Problem with battery meant it took 11 weeks to get it back on the road as the shop did not have a relationship with the bike manufacturer.
The bike however is phenomenal. I weigh 130kg and it takes me up ANY hill in Bath. There's a couple of 1 in 3s that I can cycle up one handed.
It's saved me an absolute fortune. In fact after owning it for a month, my wife wrote off my car. We just took the insurance money and didn't buy another car going down to a one car family.
I have a gold standard D-Lock that is side mounted on the frame (weight not an issue) that I use when parking up. There is also a dutch style rear wheel lock mounted to the frame I also use. The battery has a key that keeps it locked to the frame. The head unit for the eBike display is removable and I take that with me whenever I leave it locked up making the motor unusable.
Basically you're trying to steal a 25kg (55lb) bike with multiple security features and relatively unique electric parts that people would be wary of buying due to lack of guarantees.
Sometimes if I'm popping into a shop/café, I use the bike stand, lock using the dutch lock, and just take the head unit off. I'm guessing somebody could pull up in a van and just lift the bike but the opportunistic 'snatch' is so not going to get very far.
(Though if you don't need the e-thing 310€ will get you started)
As a way to get from A to B quickly, nothing beats them in a city.
I did an Air Pollution piece for the BBC comparing exposure of somebody walking, cycling, and driving in and around Bath. As the cyclist, they told me I was travelling around the city a bit too fast for the pollution monitor to get all my data correctly. ;)
I recommend spending $3k on a bike with a Yamaha or Bosch motor, it's easy to justify that crazy price if you look at the money you'll save in gas/payments/gym expenses. Most importantly, I enjoy my commute now and I feel like a part of the city in a way that car commuting doesn't give you. Also, get a pedal-assist bike not one with a hand throttle, trust me it's not better to have a throttle.
Disclaimer: My new startup is ebike related but I'm not going to be selling any bikes or hardware.
If you like your bike commute and don't mind getting sweaty you might prefer a normal bike.