Generally speaking, I use a separate event handler method for each separate function, rather than button: if your btn1 opens a file, and btn2 saves a file then I would use separate handler methods. If instead they acted as number buttons on a calculator, I'd use a single method for them all, and use the Tag property of the button to give me the value:
private void NumberButton_Click(object sender, EventArgs e)
{
Button b = sender as Button;
if (b != null)
{
int value = (int)b.Tag;
...
}
}
It's about the functionality, not about the code.