Is it wrong to have favourites??

Recently I whispered into my two year old's ear, "You're my favorite, you've moved up to spot number 1".  Although if someone had asked me where he placed on my "Favorite's List" a few months ago, I would've said number four (that being, last).  So is this indicative of how much I love them? Not at all.  For me, it's more about whose company I'm enjoying the most at the time or maybe who's been the most obedient or well behaved.  I can honestly say that I love them all equally, they each bring something different to the table.
However, I'm reminded that we all have different personalities.  There will be some people in this world who you'll get along with so easily and then there'll be others where effort is required.  I see this as being no different with one's children.  Each of my four kids have very differing personalities one from the other and I have realized that with my own, I am naturally going to get along easier with one or two types of personalities compared to another.
Before I came to this analysis I felt guilty, thinking that I did have favorites because I enjoyed their company more.  Or because we didn't "butt heads" as much or ever.  So I thought to myself, I need to change this somehow, I can't love one child more than another and I can't have a favorite.  But the more I tried, I realized it had nothing to do with love it was simply just a personality clash.  Just because they came from my womb doesn't mean that I'm going to be exempt from disliking certain traits or things about them.
However as a parent, I feel it's important not to allow these differences to control how you treat each child, as it may result in a child feeling less loved and less important.  This was, and still is, the case for me.  My Mum clearly had (has) a favorite, my older sister.  And as a child, I had a lot of resentment toward her which affected our relationship.  But now as an adult, I've accepted that this is just how it is between her and I and it's ok.  She still loves me and always has, I guess she wasn't good at treating us the same despite our commonalities, or lack of, that we shared.
So what about my "Favorites List"??  It never stays the same.  It changes monthly, weekly, daily even hourly!!  But one thing that doesn't change, is that I love each of my kids equally, and that will always remain.