So, I totally agree with the whole, tend to the older one first because they'll remember it thing, at least for now and at least when both needs are relatively equal/similar. However, when the little one is crying and the older one is being difficult it drives me crazy. My boy has never been a fan of diaper changes and is wirey and strong so it's not easy to change him. I put the baby down so I could change him and she started crying. Logically I feel like this is a situation where she just has to deal while I tend to the diaper and then I'll pick her up.
Here's where my logic breaks down and my emotions take over. My son has no concept that his sister is upset and needs Mama (even though he hears her crying and mentions it). He does not realize that his rolling about, grabbing at things etc is making the diaper change take longer and therefore making his sister keep crying longer. I, on the other hand, have a very clear picture of what's happening and get very annoyed at my son for wasting my time. etc. It;s the one scenario (or type of scenario) where I loose my cool.
Re: My least favorite part
I go through this as well.. except if DD2 is crying hysterically.. there's been a few times that DD1 will run over to her the moment she's changed and diapered (before I can catch her) and hit DD2 on the head. Almost as if she's saying.. "be quiet!" ... which leads to punishment.. which leads to meltdown.. and then I have two hysterical babies..
I just keep telling myself it will get easier eventually..