Its cliché, but you will want to retain an attorney as soon as possible! Why?
First and foremost, an attorney retained right away can obtain and secure evidence. The insurance company has a whole team of investigators, adjusters, and such who are usually on the scene immediately.
Second, an attorney will make sure that you make your way through all of the procedural barriers, making sure that the statute of limitations, the time limit when one must file suit, is not missed.
Finally, retaining counsel quickly forgoes the stress and worry of postponing the decision.