No I don't, but I don't think you can if you only have two, I guess with more it's easier to notice one you have a stronger bond with... We have 4 dogs, and I definitely have a favourite there!
My eldest child is by far the easier (so far anyway!) She's always been an easy going, delightful kid, and makes life so simple. The youngest is more spirited, and sometimes I do think "why can't you be like your sister?!" for ease of everything, but I kind of love her sassy, no shits given attitude, and I think it will serve her well, as she doesn't take any crap from anyone, and even though she's tiny, she will stand up for herself, always give her all, and it makes me proud. I worry about the older one far far more, as she is so passive, and will let others walk all over her. So then I end up thinking "I wish YOU were more like your sister!" I have a very strong bond with both, eldest will warm to anyone, and is very confident, where as younger one doesn't like strangers, and very particular about which close friends and family, she will let her guard down to, so maybe that bond feels more "special", more earned sometimes? She's very physically loving with me and her dad, loves a cuddle, which my eldest has never been like. But my eldest stole my heart the second she was born, made me a mum, and is the most genuinely lovely person I've ever met. She is the most empathetic, and kind child, and cares more about the planet and its future than most adults. I would say the love I have for them is so equal, yet so different on so many levels. I couldn't pick between the two in a burning building situation, they're both the absolute loves of my life. One makes my life easy, the other hard, but I adore them both the same.