This is a very difficult question to answer since it involves that much opinions about which is best, in any definition of best.
As a starter I would definitely go for VSTO / interop since it is easier to go, and is integrated with and maintained by the developer of both products (Office and Visual Studio).
If your require it to run on a server (with ASP.NET for example) you should NEVER use VSTO / interop.
Why?
This is what Microsoft says about it.
Office interop is not built to run on a server as a process. It is too heavy, and depends on the UI capabilities for rendering, etc. You could use Open XML for Word or EPPlus for Excel for example.
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solved Word Document Replace Text and save to a new file [closed]