Several have said “For some reason people prefer rail based systems over busses” and I can speak to that. I rode Denver busses regularly through college, and a few years later spent several months in Vienna (Wien) where I experiencec public trasportation using many modes.
Busses operate at the mercy of other traffic, and traffic lights. Because stops are cheap to build, just put up a sign, and maybe a bench or shelter, there tend to be lots of them, which further slows the trip. As a result they are always (much) slower than driving in a car. The whole time you are on a bus, you are watching cars speed past you, constantly reminding you how much time you are losing by taking the bus.
The fact that Busses add to traffic, and because they are un popular causes them to be scheduled fairly sparsely…maybe every 30 minutes at peak times, and 1/60 minutes off peak. In some respects it is a vicious cycle: Nobody rides the busses because the schedual is so sparse, and since riderrship is so low, why run more busses?
These factors cause a secondary problem, in that it is nearly impossible to keep a long bus route running on schedual. Meaning that riders often wait lots of extra time, and/or miss connections. Even when the lines are on schedual, the sparce schedualing means that even a single connection can add up to an hour to a trip.
“express” busses get around a lot of theses issues, and are in my experience (denver in the early-mid 80’s) much more utilized than “regular busses”,
Rail systems with dedicated ROW (meaning other than on-street trams) operate without regard to traffic. Stops are fairly sparce, meaning they don’t waste much time. IME (Vienna) trains arrive frequently, perhaps every 4 minutes at peak times, and every 10 minutes off peak. Even if you have to make two connections, this adds only 8-20 minutes (at most) to a trip across town.
As for trams (streetcars) The European cities where I’ve ridden them have additional lights at intersctions such that the trams get priority over car traffic. This seems to be fairly effective at keeping them moving.
One thing not yet addressed in this thread is the synergistic effect of the various forms of public transport. A subway, or light rail, system won’t be effective if there is not an effective network of other transportation to serve the stations. These “feeder” systems will be much more useful if there is a faster (subway) system available to ease longer trips. The systems in a large city will be be utilized to a greater degree if there are systems that serve outlying areas effectivly. (trains, shuttle busses, HSR, etc). “Park and ride” lots solve the problem at only one end of the trip. If you can’t complete your entire round trip back to the P&R using only public transport, then you will drive.
With this in mind, I can’t think of a city that would be well served by any single technology. You probably want at least 2 systems, and better three, that cover the range from “slow-cheap-widespread” to “fast-expensive-rare”