Mercury vapor, metal halide or High pressure sodium?

All of the four lamps are gas discharge lamps. The difference is that fluorescent lamps are low pressure discharge lamps. The rest three, are high pressure discharge lamps, so their light point is smaller than fluorescent lamps.

When you say closest, are you talking about in color output, brightness, shape, power usage ?

For color output, Metal halide then mercury (hps is orange)

Brightness, metal halide then mercury (HPS / watt is brighter then both, but it's orange)

Shape, Metal halide does come in tubular shape so does HPS, mercury might of in the past but it's hard to find them

Power usage, this really depends on the wattage your looking at, most discharge lights are higher wattage when compared to small florescent, but it is possible to get very low wattage metal halide, normally starting at 20 watts, and mercury at 40 watts and HPS at 35 watts, but you can buy a 4 watt florescent with ease.. If you go the opposite direction you can get most of those lamps in 1 kw to 2 kw pretty easy and you won't find a florescent in those power levels..