C# is a fine option if your choices are C# or Java. On the other hand, F# is safer and 3 times more concise language that can do everything C# can It interops perfectly with any C#/VB.NET libraries. I'd think long and hard when writing any new C# code, and defend why you need to reduce your possible solutions to only those C# supports, when you could have the ability to do everything C# does and more with F#.
For me personally, conciseness of F#, it's tendency to use short words, cram things together and overload operators actually make it less readable. I like many of the features F# has and am happy to see how they are slowly migrating to C#.
If you want to get paid...use C#, if you want to get paid less...use vb.net, if you want to be right use F#. This is outside of the startup discussion here...but it is the general rule for MS developers. All three languages are comparable to the junior to mid level dev.
