By "with a throttle", are you looking for an ebike classified as a bicycle (up to 20mph) that can go on bike trails, etc., or a higher speed pedelec?
As for most reliable... there aren't any comparative studies of ebike reliability. I went with Pedego, which has a shop near me as well as a 2 year parts and labor warranty. If reliability is important to you, I suggest you get a bike that will be supported by a local bike shop near you. Then, when there is a problem, they can fix it and may even provide you with a loaner if they have to wait for parts. Be sure to ask any shop about service-related policies, etc.
I'm sure others will chime in about their own experience with their ebikes.
For obvious reasons ebikes are way more complicated than non-powered bikes and it’s possible, but not likely, for strange problems to occur. Unless you like to “tinker” with things pick an established company. Yes you can save lots of money with only online orders or someone working out of their garage but where are they should problems arise.
This is a great forum and lots of others will have experience similar to your situation.
I agree with the suggestions made by ebikemom and Marci jo. Another thing to consider is the ebike laws in your area. Bikes with throttles are class 2 or class 3. If the class system is in use where you plan to ride, check to see if this class ebike is legal.