Let's pick a scenario

I have written an epic fantasy novel (in the 6th-7th draft stage, I lost track...) and was extremely lucky to establish contact with the sci-fi &fantasy editor at a major Australian publisher. They were happy for me to send them my manuscript which I did, however they resigned shortly after. Before leaving they gave me some good feedback, asked me to trim from 240,000 words to 180,000-200,000 words, and then resubmit to their replacement. Two days ago I resubmitted and am now wondering about agents and what the best next step is for me. Should I start looking for an agent using the feedback I have so far received and the fact my manuscript is currently with a publisher? Or should I wait and see the response (I know it is highly unlikely I will be offered a contract but I will at least have a great deal more feedback) then ask the editor if they have a preferred agent they have a good working relationship with and get an introduction from there?

There is absolutely no harm in looking for an agent now, and there's also no harm in waiting until you hear from the publisher. Let's look at the different scenarios, though, just to make sure ...

A. If you get an agent and then the publisher doesn't want to publish it, you will have someone already in place to support your writing and help you find the right publisher for you. 

B. If you get an agent and then the publisher does want to publish it, you will have someone already in place to negotiate the deal for you and, hopefully, provide editorial support (depending on the agent - not everyone does this) and give advice.

C. If you don't get an agent and then the publisher doesn't want to publish it, well, you're in the same position you're in now.

D. If you don't get an agent and then the publisher does want to publish it, you have about a week in which to find an agent (if you want one at that stage) before the publisher starts pressing you for a response to their offer.

If you ask the publisher if they have a preferred agent they are likely to tell you that they don't, as it's unwise for publishers to play favourites lest they incur the wrath of the well-known harridan agent cabal. They may unofficially suggest someone but this does not usually happen. Your best bet for finding the right agent for you is to query agents who represent authors in your genre or authors who are on this publisher's list. Sci fi/fantasy is not represented by a lot of Australian agents so you probably won't have to send a lot of queries.

Good luck! And good on you for doing that many drafts - many people fall well before that hurdle.