Even now, I can't believe I just wrote that title. Even stranger is that I'm completely serious! Being in the query trenches, though demoralizing a lot of the time, can be a tremendous way to gain insight into the process to know what you want from an agent that you otherwise wouldn't have known.
Honestly, my idea of a "dream agent" has flipped 180% from what I thought when I started this crazy process about a year and a half ago. In fact, the agents I'd identified back then as ones I'd most like to work with aren't even ones I'm querying now! My priorities have changed, my knowledge has changed, and my understanding of the process has been thoroughly upended.
Here's what I've learned: getting a "big" agent with a lot of splashy deals doesn't mean they'll be the right agent for ME. Personally, I need someone who is a good communicator. I need someone whose list isn't so full that I won't be a priority (I write fairly quickly, and I need someone who is okay with me keeping them busy and not waiting forever to go on sub!) I've also learned there are certain agents and agencies who are really vocal with their politics and narrow minded about who they want to work with. Even for the ones whose politics I agree with, this is a turn off for me. I want my professional relationship to be separate from how I vote.
I have other criteria I've worked out on who I query (which is far more selective than before), but I'll keep those to myself to avoid offending anyone :)
Basically, what I want others who may (or may not) read this to get out of it is not to let yourself be too sad when you don't land your "dream" agent. After all, your dreams may very well change!