Developing X-Tension - what is the best 'platform'?

I’ve developed some X-Tension using VisualBasic for Tamino 4.1.4.
Upgrading from Tamino 4.1.4 to Tamino 4.2.1 and registering these existing X-Tensions lead to the following warning:

Deprecated feature used: Usage of COM server extensions (INOXMV8550).

Question is: What is the preferred way to solve this issue?
(Is it transforming the VB6 to .NET, or anything else).

Direct C++ or Java extensions are recommended.

COM is deprecated. This means that no new features will be added to the COM infrastructure.