The answer to this does depend on your personal circumstances and because there are many things to consider then you should definitely see a Solicitor for advice before making your final decision.
However the first thing to think about is whether you think you will reconcile with your spouse. If you do then it is probably better not to go down the divorce route!
Another decisive factor should be how secure you wish to make any financial agreement. When you separate you can agree financial matters and even have a Deed of Separation (or Separation Agreement) setting out the agreement. However this is not a Court Order and is not necessarily legally binding upon both of you in the future.
On the other hand when you get divorced you can obtain a Court Order which sets out your financial agreement and once sealed by the Court is legally binding on both of you. This Order can be made by consent so there is no need to attend Court and for a Judge to make a decision upon your behalf.
It is possible to have a Judicial Separation which is a far more formal separation and within these proceedings you can obtain a Consent Order. However this means that your separation is dealt with by the Court and is not a route often taken by separating couples.