I was lucky enough to get offers for a call with several agents recently. One of the agents I talked to said she only submits manuscripts to editors on a list made by the writer, she doesn't do any list-making herself. Tbh I hadn't thought that far ahead and if she had asked me I wouldn't have known what to say.
As a querying writer, should I have a list of editors prepared?
This is not something I've ever heard of before. In my experience, agents usually put together their own list of editors to pitch any of the books they acquire to. They have existing relationships with these people and meet with them regularly to keep on top of what they are looking for. In fact, one of the main reasons you want an agent is because they have access to editors an writer doesn't have on their own.
An author can't be expected to know who the right editor for their book might be. Sure, you can find the name of the editor of book you love or one you feel is similar to your own, but that doesn't necessarily mean that editor will be looking for a book like yours. Maybe they already have a similar story on their list. Maybe they have stopped looking for books like the one you read because they sense the market is cooling for that type of story. Maybe they don't even work for that publisher anymore.
These are the things an agent should bring to your partnership, the things they are the expert in. And once you both feel the book is ready to go out on submission, she should be able to show you the list of editors she is going to pitch it to. She should also explain the reasons why she's choosing these editors and how she's going to pitch the book to them. This is the point you need to decide if you want to hear all the feedback she gets on your project as it comes in, or if you'd rather just hear if they passed or were interested.
I think there should be an opportunity for you to make a suggestion if you have some information or a relationship with a certain editor, or a very strong feeling about a particular publishing company you feel would be perfect for your book, but the onus should not be on the author to decide who the book is submitted to. That's the agent's job - what you will be paying her for when the book sells.
So, I see that particular question as being a red flag. The agent's job is to know the editors at various publishing houses and be on top of their likes and dislikes. Any agent who asked me to do her job for her, is not an agent I would want to sign with. If she doesn't want to do this very basic function of her job, who knows what else she might decide she doesn't want to do?