I have 3 and the same as everyone else, I love them all equally but for different things and at different times.
My DD (11) is so much like me it's scary. We like the same films, music, books, hobbies and she is my only girl which means I understand the changes she's going through etc. However, she is also a bundle of hormones and at times is a right nightmare. We often have slammed doors and how much she hates me.
My DS1 (8) has SN. My DH jokes that he is my favourite but as a pp said about her DB, it is because I need to help him more than I should an 8 yo, guide him more, explain things more and the pride I feel when he does something I never thought he would do is immense. However, because of his SN, he is harder work and sometimes he drives me mad.
DS2 (3) is so cute as he is at my favourite age of child and loves cuddling. However, he is 3 and capable of many tantrums and his favourite word at he minute is poo poo head. Some days, we spend a lot of time at the naughty corner.
I like the one who is behaving at the time. I can't see how you can love one of your own child less on a regular basis. I am currently ttc #4. And I know I will love/like/dislike them the same but different too.