Lets understand the difference via this example

int i 0;
MessageBox.Show(i.ToString());
MessageBox.Show(Convert.ToString(i));

We can convert the integer “i” using “i.ToString ()” or “Convert.ToString” so what’s the difference. The basic difference between them is “Convert” function handles NULLS while “i.ToString ()”does not it will throw a NULL reference exception error. So as good coding practice using“convert” is always safe.

http://kalitinterviewquestions.blogspot.com/

.ToString() method lets you convert any value to a string.

While convert.ToString() method uses the Convert class which provides shared methods that you can use to convert value with any data type to any other data type.