Model railway tracks fall into two categories, raised and ground level.
Although many people run on ground level for the smaller gauges, even down to 2 1/2" gauge, my personal view is that raised track is best for 3 1/2" gauge and below, and ground level for 7 1/4" gauge and larger.
5" gauge can be either, and whilst there are some excellent 5" ground level tracks which adhere closely to prototype practice and standards, I prefer raised track for this gauge, unless the model is of a narrow gauge prototype.
Raised track is more stable as the centre of gravity is lower.
Ground level tracks can have points (difficult with raised track) which enables a more complex layout to be constructed, and they look much more realistic.
Rail can be aluminium or steel, and in the latter case, is sometimes made of square or rectangular section.
Steel rail wears well, allows track to be welded, and, size for size, will take a heavier loading, but unless it is in frequent use, will quickly rust, and when next used, the rust particles will be lifted off the track as a fine duct which will adhere to the locomotive and rolling stock.
Aluminium rail has to be supported at more frequent intervals, especially under joints, and needs less
It is often claimed that a given locomotive will haul a greater load on steel track compared to an aluminium one, as the latter tends to be "slippery".