Well it sounds like you do independant work so it may not matter which you use as the client usually doesnt see the code.

Going from VB6 to VB.NET itself is difficult to un-learn some bad programming habbits. So C# may be easier to learn for you but in my opinion its slower as you have to type in the correct case and a few minor things take a little longer to get used to as compared to vb.net. I am glad I went from VB6 to VB.NET as that worked best for me.

Spend a little time on each language of the same project to be able to see the differences for yourself.