They are the same int variable for the class however the first one since its a static int, it would be accessed from the Class and can be altered and any instance of it would have the same value.
public static int intId;
The second one will just be accessed by instances and its an unique value per instance since its not static, but it can be accessed by anyone since its public.
public int intId
{
get
{
return intId;
}
set
{
intId = value;
}
}