We have a mix in Seattle of electric trolly buses that drive on the road, and light rail. Both have advantages and disadvantages but in practice rail is much nicer, at least out here. It has fixed routes that never change so you can rely on it, the bus routes change too often to depend on it if you need to get to and from work at a set time. Rail is more power efficient due to lower rolling resistance, and perhaps most importantly rail is a dedicated route with right of way whereas the electric buses sit in the same gridlock with all the cars. The unfortunate thing is that they didn't put in the rail 50 years ago when they started talking about doing so, instead they waited until traffic became unbearable and costs were much higher.
When I've visted Los Angeles and Chicago I made extensive use of the light rail/subway systems and they work very well, in urban areas it beats driving any day, and I'm a car guy, I just hate driving in downtown gridlock.