Both are equivalent.
I remember when I used to code in C, I preferred 'if (5==a)' because it guarantees that I haven't typed 5=a accidentally as the compiler would throw error. This would not happen if we write 'if (a=5)'. Though it is a typo, it would not generate any compiler error and would go unnoticed.
But, in C# it is not the case. There is no logical reason to write 'if (5==a)'. If we had written 'if(a=5)', the compiler would throw an error. So in C# use 'if(a==5)'!
