Industrial Ethernet is a pretty broad term. It is true that "Industrial Ethernet" is built in, but that doesn't exclude Modbus TCP. Its mostly just a buzzword that means it is an Ethernet device used in an industrial environment instead of an office one.
The most important question to ask yourself is this:
What are the communication requirements?
Strictly speaking, the PLC doesn't communicate with the PC itself, it communicates with the PC software. What software/type of software are you running? Does it have communication limitations? Are you writing it yourself from scratch?
If you are buying a program, and it has a pre-existing communications driver for your PLC, you should probably use that.
If you need cyclic communication with high polling rates (<10 ms) and deterministic behavior, you probably need to use Profinet. This may require special cards or software on your PC. This wouldn't require any special PLC programming except to copy data to from a new IO area, but it would require some changes to the HW configuration. If you need to send more than 1440 bytes of IO data, this probably isn't an option.
If you need cyclic communication with a low polling rate (>100 ms), OPC is definitely a good bet. You would need an OPC server package that supports the 1500, which makes data available. Your PC Program would then be an OPC client, which accesses the data from the OPC server. Siemens obviously has OPC servers that support its products, and Kepware's OPC server supports just about everything and is probably the most commonly used. This probably wouldn't require any PLC programming except possibly to copy data into and out of a DB reserved for communication. The HMI in your system, if one exists, may already support being an OPC server. If your PC package is something like an HMI or monitoring system, then OPC probably makes the most sense.
If you want acyclic communication, meaning you are sending messages (potentially very large) based on system events instead of time period, then TCP is probably the best solution. It requires programming on the PLC end (look at T_SEND_C/T_RECV_C).
Modbus TCP is also an option, but the only advantage it has is being free/cheap. It would probably perform comparably to OPC, but isn't quite as widely used. Many PLCs support Modbus TCP, but it is a lot less common in PC software.
