The basic argument for different track designs will be based on the bottom line - cost; cost of installation and cost of maintenance. There are however, other issues such as environment - noise, dust and vibration - or engineering issues such as space, location, climate and the type of service intended for the track.
There are a wide variety of track forms and systems incorporating some form of concrete base or support which doesn't need ballast. Almost all of these require less depth of construction than ballasted track. However, the accuracy of installation must be higher than that needed for ballasted track. Slab track will not be adjusted after installation but ballast can be packed to align track as required.
The ability of ballast to allow track realignment is one of its most serious weaknesses. The lateral movement caused by passing trains on curved track is one of the major causes of maintenance costs added to which is the crushing caused by axle weight and damage due to weather and water. Ballast damage leads to tracks "pumping" as a train passes and, eventually, rail or sleeper damage will occur, to say nothing of the reduced comfort inside the train and the additional wear on rolling stock. Apart from regular repacking or "tamping", ballast will have to be cleaned or replaced every few years.
Another aspect to the ballasted track design, is the dust which is caused during installation and as it wears or gets crushed. It does however, offer a useful sound deadening quality.
Fixed track formations using slab track or a concrete base of some sort do not suffer from such problems. However, the installation of slab track is reported to cost about 20% more than ballasted track. To balance this cost, the maintenance costs have been quoted as reduced by 3 to 5 times that of ballasted track on a high speed line in Japan.
If low levels of use are foreseen, or if low capital cost is a more important requirement, ballasted track would be the choice. For a heavily used railway, particularly one in a structurally restricted area like a tunnel or viaduct, non-ballasted track must be the best option on grounds of low maintenance cost and reduced space requirements.
However, care must be taken during design and installation to ensure the best out of the system.