Since you've worked on VB6, you'll find VB
.NET familiar. Familiar, that is all, 'cause, VB
.NET works in an entirely different way otherwise. I would suggest VB
.NET 'cause of the ease with which you can convert data to XML with techniquies like DataSet's XML serialization.
If converting to XML is a small part of the entire thing is not being done too much or too often than you can safely stay with VB6 withoug missing much.
C# would start a whole new learning curve for you so stay with VB
C# is THE DE FACTO .NET language though.
So I say if coversion to XML is something that sounds like a cumbersom job to you, you will find refuge in .NET, at the cost of some effort you'll have to put in to get aquainted with the new environment. If XML coversion is no problem for you stick to VB6.
Database connectivity is somewhat different in .NET and may take some time getting use to. It is easy though.