What is the difference between oracle.dataaccess.dll vs oracle.manageddataaccess.dll and what are the advantages of managed dll over data access dll

The main difference is that oracle.dataaccess.dll needs the local non-managed DLL Oracle Client installed to work. This is a .NET wrapper for calling the native library.

While oracle.manageddataaccess.dll is a pure .NET implementation of the Oracle protocol. So you only need the .NET runtime installed in order to connect to Oracle. No local Oracle client needed.

I don't know how the two compare performance wise. In theory, the oracle.dataaccess.dll should be faster but way less portable. While the oracle.manageddataaccess.dll should work in any computer despite not having the local Oracle client installed (which is a pain to install and maintain BTW).

I would definitely use the oracle.manageddataaccess.dll. Its performance should be good enough for 99.99% of the cases. And you'll avoid the hassle of an extra installation/configuration for your .NET project to work.