From a power consumption point of view, which should I use: SSR or Relay?
A common relay may need 350 to 400 mW, and the current will depend on the nominal voltage. You'll be able to decrease the voltage after the relay is activated, however, and often go below 100 mW. But not all relay datasheets mention the minimum hold voltage.

An SSR has an IR LED which drops less than 1.5 V, often as low as 1.1 V, and may have enough at 10 mA, then that's less than 15 mW, far less than the electromechanical relay.

But while the SSR is more economic at the driving side, it will lose much more energy on the load side: a voltage drop of 1 V (optimistic) at 1 A is 1 W, while the relay with a resistance of200 m&Omega; will dissipate only 200 mW at 1 A.