Also consider the other consequences:
A relay provides isolation between the control (coil) and switch contacts, a triac does not,
A relay gives an almost perfect on/off control with almost zero 'on' resistance, a triac will drop at least 0.6V across itself.
That ~0.6V drop multiplied by the current will give you the power it dissipates which might be higher than a relay.
For many applications, a triac and opto-coupler combination will work better than a triac alone, it buys back the isolation and with a suitable opto can also help to reduce inrush current and EMC problems.
Brian.