See this:
https://stackoverflow.com/questions/507291/should-we-select-vb-net-or-c-when-upgrading-our-legacy-apps
Of course, C# vs VB.Net is just one part of it.
For example, another thing to consider are if you want to use this opportunity to move these apps to an intranet, if you haven't already. Or how deep do you want to delve into microsoft's stack. Is Winforms enough or do you want to use WPF, for example.
