I'm more into the fitness aspect riding. I use mine to help extend my riding distance and time. I ride a Trek FX+ of which I'm fairly happy. It uses a Bionx system which can be bought independently and added to an existing bike. The Bionx bought independently can employ a throttle however the system is a little expensive.
My advise is to look around and to find the system that best fits your needs. It seems like you are taking the first step. Good luck
xtracycle, electric recumbent, downtube folder and more
They are fun but expensive and you usually have to be willing to fuss with them unless you spend really big bucks. Just buying a better bike will give you more thrills than electric and for less money I would guess. I would suggest trying both new bikes and electric bikes since you are probably not in a rush to get something. It can be difficult to get a good electric bike because most electric bike companies go out of business every few years and you can't get parts which is why putting a kit on a bike is still a good way to go if you like fiddling around with stuff.
If you are going convert with a kit, you can't go wrong with a kit from clean republic, who claims 5 minute conversion time. which is almost true, if you didn't have to slightly enlarge the dropouts for the motor axle. complete kit is about $400, including batteries and they are located in Washington. I was very satisfy with mine. I believe there is a video too. uses a Bafung motor and sla batteries to start with.