Which is the most preferable PLC for industrial purposes ? give reasons for saying so?

It obviously depends on the clients requirements.

Both technical and budget has to be considered.

If the sensor inputs are minimum and consist of only digital inputs then Allen Bradley Plc are a good option.

If analog data has to be encountered and if there is possibility of future expansion of industry then Siemens and GEFANUC can be considered.

ABB also provide high end plcs

For small budget Chinese made Delta plc can be considered.

working with generators , there are many types and brands that you could work with .

Comap is cheap and somehow dependable and easily to deal with .

Siemens is great but somehow extremely sensitive to fluctuations .

ABB is good . powerwizard . and deepsea are also dependable but they all depend on the working condition you use them within  

Siemens

Honeywell

Rockwell but I do not recommend for Gulf area due to the customer service leakage

That depends on different factors, like:-) Financial ability.-) Availability of PLC parts in the local market.-) Familiarity of a PLC in the local market (local people who can support).-) Application of a machine (does an application really require an expensive PLC ?).-) Programming flexibility (plays a strong role in repairing or modification time).

depends on the requirement currently mostly used in market ABB Siemens , mitsubushi

All PLC is fine. But it is depend the I/O and industry based. Because PLC having simplex PLC & redundancy PLC. Best  PLC Brand  : ABB ,siemens, Allen bradley, mitsubishi.  

in critical applications most uses siemens  plc ,in normal application  can use any brand . 

It depends on your application. You cannot say that this is a preferable PLC or not

Selection of PLC depends upon many factors such as

1.Number of inputs and outputs:-If we are having an application which has less number of I/O then we use micro type of PLC instead of rack type PLC.

2.Operational Speed.

3.Cost:

4.Make

Siemens Is most  likely used and cud be the most efficient one as its leading the market for years 

Mostly it depends on customer requirements and budget, but as per my opinion Siemens is best PlC for industrial purpose because if we want some expansion in future then it is easily possible in Siemens and it is very reliable.