SVC is based on thyristors without gate turn-off capability. SVC used in electrical power transmission.
Firstly, SVC's are normally used at high voltages, where SCRs are the cheapest available option. They are rugged too. They are one of the few devices with reverse voltage blocking capability, which is needed in ac line switching applications.
Secondly, given a device with turn-off capability, one cannot interrupt the line current abruptly, sine the energy stored in the line inductance will immediately generate a high voltage kick across the device being turned off, damaging it. Thus, in applications like SVC where the SCRs are used as switches for the capacitor banks, there does not appear to be any cheaper & better switch.
Of course alternative technology like STATCOM are available, but they are expensive as of date.
In terms of COST u can prefer SVC and in terms of Better Performance prefer STATCOM if u need both go for optimization techniques. using those technique place an SVC where u need less cost and place a STATCOM where u need better performance than cost.
