The API functionality is identical.
Personally, I'll pick a true object oriented language such C# over VB every time.
Not only API functionality but also the .NET framework CLR is identical, so when you call "VB.NET's not object oriented" than you have to say the same about C#.
C# and VB.NET are fraternal twins, with the difference that VB implements some special functionality to support "global modules" (would be static abstract classes in C#), offers an additional namespace (Microsoft.VisualBasic) which you could also import into C# projects (but you shouldn't - even well-respected VB programmers don't use it), and - of course - the different syntax.
The only thing you can do with C# that VB doesn't support is the opportunity of writing unmanaged code with pointers.
So the question whether you should develop a SolidWorks AddIn with C# or VB can only be answerred: Choose which you like or which you are more familiar with. VB developers have the "advantage" that they are capable of switching to "C# developing" while most C# developers seem to have problems taking VB almost into consideration, so using C# from the very beginning could be better if you plan to keep the program mostly maintainable.
But to say "C# is object oriented and VB.NET is not" is nonsense.
Microsoft has tried to kill Visual Basic.
I prefer C# for its 'pithiness'. I found it about 1.5 times quicker in pure typing and the code looks more readable. But there is nothing which is possible to do in C# but is impossible to do in VB.NET.
I did a prototype application in SolidWorks using both C# and VB and i agree to what you say, writing it in C# was quicker than in VB ( this could be because i come from C++ background ). But i personally found it more readable as well.
I think what Ralf mentioned is very important, we do not have many VB developers and most of our people come from C++ background. so going ahead with C# makes more sense since both the languages are similar in style.
Thanks for your response.
I use C# in most of my program but used VB in Solidworks add-on(due to that it was upgraded from a SW Marco and I did not convert it to c#)
I only see a few pro on vb that I don't know how to do in c#(ex clipborad access)
If i could i would convert my add-on to c# but It is grow to big to be worth my time.
I do cross over I have 11 project in my solution (visualstudio 2012) and 8 are VB and 3 are c#
so you can get the best of both worlds if needed