I recently parted ways with my first agent (amicably, of course) and have had requests from editors at mid-size and larger houses to see my future work. I have a manuscript that has been polished and is ready for submission. Should I send to those editors while I'm querying, or should I wait to see if I can secure an agent before doing so?
Don't send your work to editors before securing an agent. If you do so, you'll find getting an agent is MUCH harder because you've trampled all over the crime scene and contaminated the evidence.
When an agent takes on a project, she puts her knowledge and expertise to work on your behalf. That might mean revisions to this "polished" manuscript and it certainly means a tailored submission list. All you know are the editors who've said they'd like to see you work. What your agent will tell you is which editors SHOULD see your work.
Don't let your impatience get the better of you. I posted about this recently but it bears repeating: I'm not keen on stepping in to a project after it's started, and once you've sent your book to a publisher, you've started.