Which plc is better, siemens logo series or mitsubishi?

I think there no worse or better. This is long process but here is what i have in mind now: 

you should think about:

* what stranded you need for your process and which one will meet these requirement.  

* your process  compatibility with the plc. (for example some will not operate servo valve and you need addition system)

* price 

* availability of spare part 

* availability of service 

*life span for the product : There is no use in case you installed a system where the company officially saying they will service  the product in one year and then you have to upgrade. (believe me this happen)

*what is already installed in your site: having one card as spare then used in two differed machine with the same model of PLC will make a deal in stock spare. This opposite of having two system where the company should make two spare with training in two systems for worker.

It depends on the automation requirement, cost, complexity, size

All of them are good and they do the jib you give to them.

but there are somethings you can depend on for taking differences :

-Cost

-maintenance

-simplicity ... etc

Well, there are many factors to determine which brand/type/size of PLC you need to use such as but not limited to the following:

• Type of Application
• environment.
• Cost.
• Brand service support.
• Brand documents.
• Brand utility tools.
• etc.

regarding what you mentioned about Siemens Logo & Mitsubishi; Siemens Logo is categorized as a small PLC (limited I/O's). Mitsubishi has many types of PLCs which are categorized as small, medium &  large PLCs and also Siemens has as well.

Both the PLCs are better .its unethical to compare both the PLCs.

It depends upon system requirements

Both the PLCs are better or non-user friendly depending on the type of process we opt for. So its unethical to compare both the PLCs.

It depend up on the application .... siemens logo plc  is a small PLC it can be used for small Projects,