If you're looking for a lock for relatively brief use for stops (coffee, lunch, etc.), a combination of a good u-lock and a braided cable or chain is a good one. I have the "Kryptonite Kryptolok Series 2 Standard Bicycle U-Lock with Transit FlexFrame Bracket (4-inch x 9-inch) with 4-Foot Flex Cable". I carry the lock and cable in Ortlieb panniers that are mounted on my rear rack (I got the panniers recently from REI on their Anniversary Sale, and they're fantastic -- I went with the Sport Packer Plus model).
To use the lock and cable, I loop the cable through itself around the rear wheel, run it up and through the front wheel, then attach the u-lock through the frame and the flex cable loop around a bike rack ("staple" bike racks are the most common ones in my area). I then remove Yamaha display and seat+post, and put them in my panniers which I then take along. I've been meaning to get some sort of theft resistant seat post clamp, but haven't yet; the quick-release on mine makes it way too quick and easy to steal. I will also take the battery if I'm going to be out of sight of the bike for any length of time. I just feel like it attracts too much attention, and part of me feels that a semi-knowledgeable thief will pass on stealing an e-bike without a battery and display.
My only complaint with the lock is it can be a bit fiddly to get the key in, but it gets easier with practice. If you keep any lock out in the weather, make sure you lubricate and maintain the cylinder.