Which is better, controlling electrical motor by PLC or Arduino or Micro-controller?

Generally speaking, this depends on the use of your motor, whether it is for occasional or industrial use. Notice that Arduino is a simple microcontroller based circuit.I found here a nice post which explains the difference:

No Arduino is never going to replace PLCs. You ask why?

• First of all if you follow link about you'll find that the industrial printers in the link about use 5 arduinos, and why is that , because they have low I/O count. Event the most advanced arduino has I/Os that max out at around 100-150(approx). But even a small industry will easily have more than 100 I/Os. Now you may say we can use a number of Arduinos to suffice for lack of I/Os, yes we can , but ask yourself what will be easy to manage(debug or program ), PLC with a single CPU(there is always a second standby CPU in  them !!) which will have all the program or, A number of arduinos with the whole program divided into each and they all communicate and synchronize using protocols like I2C,SPI or at max Serial at 115200 baud, which is horribly slower than those used by PLC like Modbus.
• Second problem is communication protocols available, and problem being they are slow.Why? Because, when you have at least 1000 I/Os to handle then you will have around 2000+  process parameters that need to be communicated to the Operator console at at least 100 to 10 Hz rate. And at the same time they also need to be communicated to control equipment/hardware/device at much higher frequencies like tens of thousands time. And with slow communications available it will most likely result in a blown up Boiler or a Turbine breaking due to excessive vibration and all that not counting the life casualties and monetary loss and all sorts of accidental hazards.
• Third point being Reliability. What if just one of the Arduino malfunctions which is a very obvious possibility because we need to reset it when it hangs and again it works perfect , but this is not tolerable when you are controlling machines worth Billions of rupees/dollars. PLC always have a standby CPU  that takes over when primary CPU fails or starts misbehaving.
• Fourth reason being, PLC is programmed using ladder logic which has been understood and used by engineers and technicians for decades , but on the other hand Arduino has its own language(not even C). And yet again ladder logic being graphical is easy to edit and debug.Teaching a new language like Arduino will be cumbersome .
• Fifth reason being that , if you are setting up an industrial plant worth millions of dollars then you wouldn't want to give its control in the hands of a device that come under 100$ !!. So its the trust factor at last ,PLCs have been here for long and they are going to stay.

And at last if you design an Industrially robust Arduino based controller from scratch, keeping in mind all the industrial norms then again it would be nothing but a PLC that is slow at communication,has low processing power,is less reliable and understand Arduino language. It may be useful for really small industrial application like in situations where the application is not critical and reliability is not big a deal, But yet again its far from replacing PLCs.

Both of PLC & Arduino are kind of Embeded System Programming  but the Interface & Programming Language is different .

it depend on the Application . if you Arduino or any Microcontroller kit is general Purpose Application .  but PLC is dedicated for control purpose

So if your motor need advanced type of control like fuzzy logic or real time process so you need to use microcontroller

if you need to control simply with sensors & timer use PLC because it is easier & Suitable for industrial  Conditions more than Microcontroller

I apologize this is not my specialist