Usually stabilizers are pure sine wave as they only "clean" the outlet power being supplied.
There are a number of stabilizers (or voltage regulators) - the ones available in Pakistan are the Relay type, Switching type (which use chips (MOFSETs) to do voltage regulation) and Servo motor (linear) type.
Relay type: Uses a transformer and uses relays to give a range of "appropriate" voltages based on input voltage range. The relay switch can "dirty" the electricity being supplied and is used for low-sensitivity applications like Fridges and Deep-Freezers. Are available quite cheaply (upto 10k)
Switch Type: uses MOFSETs. Are relatively expensive (3000VA can cost upto 10-15k) but as per personal experience, due to the "quality" of the circuits in these models, they are risky as they are not built with protective mechanisms in mind
Servo type: uses a transformer with a motorized arm shaft that is engaged to output constant voltage. These are the best available in the market and are very expensive nowadays and are most suited to sensitive electronics)
Stabilizer capacity is essentially determined by how much current it can supply.
VA is essentially voltage x amperes, and Power (measured in Watts) = V x A x PF. Power factor essentially represents the efficiency of a particular circuit - you can assume 0.8 since that is typical.
To calculate the appropriate VA for the stabilizer, multiply your appilance's input voltage (i.e 220V) into the max Amps that appliance takes (check the power-plug or adapter, it should mention it) and multiply by 0.8. Do this for all electronics you will plug into the stabilizer and you'll get your requirement (you can connect an extension cord to it). Keep in mind future expansion and always over-size your VA capacity vs. your actual requirement.
I have personally gotten the following model for my PC:
Stabimatic SXD-2000C 2000VA AVR Stabilizer