Do you need to know whether object a is of a derived class from the class that another object b is of? Or if they may even be of the same class?
The following little code snippet tells it..
program dummy;
var
a,
b: TObject;
begin
// some code to assign the pointers
// ...
// now evaluate the RTTI of two instantiated objects
if a is b then
ShowMessage('a is derived from b or same class');
if a.classtype=b.classtype then
ShowMessage('a and b are of the same class');
// alternative to ClassType comparison (slower!)
if a.ClassName=b.ClassName then
ShowMessage('a and b are of the same class')
end.