Which contactor to choose for a 3 kW single-phase load

Hello! First of all, the difference is in performance. All three of these brands are, in principle, not in a very budget segment of the market. Especially ABB and Schneider. They also have different categories of use (Schneider has AC-3, ABB has AC-1, and Legrand does not understand).

AC-1 is a load such as heaters, incandescent lamps, without inductance and without starting currents.

AC-3 is a load with significant short-term overloads, such as direct starting of electric motors with Short-circuit rotor, switching off the motors (possibly with repeated switching on or counter-current braking) and so on Further.

If it is simpler, then the AC-3 can withstand more rigid switching.

The first (Schneider) is a conventional open contactor. The one from ABB is already a modular contactor on a DIN rail, I believe that it will turn on quieter and not buzz so much (although I'm not sure about that). If the first two had 3 poles and 1 contact block, then the third, Legrandian, had two poles, themselves count the number of terminals - there in the photo you can see that the coil contacts are from below, above them there are 2 more contacts and 2 above. In total there are 2 groups of normally open contacts.

p.s. And ABB itself is expensive (although usually on a par with Schneider).