The eBike market is young and has recently exploded in popularity in the past couple of years (most likely due to lifestyle changes related to COVID). So what eBike should I buy, where should I buy it, or should I make one myself?
You really can't go wrong buying a name brand bike from a dealer. It will be supported by the manufacturer and you will be able to get support from the dealer. Common brands include, Giant, Trek, Specialized, Cannondale, Gazelle, etc. You will probably pay a bit more, but it will probably also be an easier/safer experience.
There are a lot of new brands that are selling direct to the consumer. Some of these brands have better reputations than others. This list is by no means exhaustive, but some brands that have good track records include: RAD Power Bikes, Aventon, Electric Bike Company, Charge Bikes, Priority, and Ride1Up.
Consider when you buy a bike, if something on that bike breaks, can you (or a bike shop) get replacement parts for it? This is often a difference between name brand, reputable companies, and cheaper bikes. If a part breaks and you can't easily replace it, you will have to do a DIY conversion or buy a new bike.
You can also build your own eBike, or modify an existing bike. There are kits that make it as simple as changing your front tire and attaching a controller. Or you can build the entire bike yourself using a combination of parts and kits. More than likely, you will be able to build your own eBike for considerable less than a name brand bike, if you are good at Do It Yourself. There are many internet resources to help you. I am guessing however that if you are reading this site, building your own is probably not for you.
If you have the opportunity, test ride a bike from a dealer, rent a bike, or try a friend's bike to see what it is like.
Recommendation: If you can afford it, buy a name brand from a dealer. You will get a great bike and it will be supported. If you need to save money, purchase from a reputable vendor with a known, proven track record. eBikes can be hard to get right now. Make sure whatever you are ordering is in stock and ready to ship.