Is there any reason why I might choose an EM-relay rated at coil-voltage of 24V or 12V, over one rated at coil-voltage of 5V, all other specs like contact max. current, switching voltage, life etc being same. The only other difference in specs that I see are coil resistance, and contact material.
Most of the circuit schematics I found online, seem to use 12V relays, and very few use 5V relays. Given that low coil-voltage rated relays have lower coil-resistance, I'd only believe that one wastes lesser energy in switching and holding the relay, by using the 5V one, compared to the 12V one.
PS> By default I might order the 5V part, as I have quite a few 5V power supplies at hand, and none rated 12V. But if there's a good reason to use 12V EM-relay, I don't mind. Both parts (5V/12V) cost same.