A comment from MarkJ made me re-read the Q, and from "replacement" I now understand this is likely a re-code/new version project, not a start from scratch... the original answer below is not accouting for that.
Meanwhile, MS says it's suportting a core runtime file of a language that has no roadmap or committed resources (?), so bottom-line of my answer still stands: vb6 stopped, new projects can go Python, vb.app, java, c++, C#, whatever.
Original:
None. VB6.0 reached its End-Of-Life. Go Python! or Java, or C#... never vb .net, because it's tons harder/dense than Java, not VB6.0 syntax in the slightest, and the learning curve is just a notch under C#.
P.S. It's so interesting to have negative votes because I trashed vb .net when compared to java or c#.
I wonder what these guys would think of me, being a former vb6 programmer, and not moving to any of the .net flavors.