I would agree with the previous response that generally, architects and developers have a preferred planning consultant that they use regularly. With regards to the benefit of using a local consultant/firm, I would say that this depends on the nature of the appeal. For a domestic extension for example, familiarity with local planning policy would probably make a consultant who has carried out work within the Local Authority planning area previously a logical choice. That having been said, a good consultant should be able to familiarise themselves with relevant extant local policy fairly simply and form a judgement as to how this conforms to legislation, the National Planning Policy Framework and Planning Practice Guidance, all of which may be more of an issue at an appeal than during the initial application.
A couple of other points, firstly don't forget that an appeal must be submitted to the Planning Inspectorate within 12 weeks of the date of the LA decision notice (28 days if subject to an Enforcement Notice). Secondly, an appeal may not be the best option, you may be able to overcome the grounds for refusal by submitting a revised application to the LA.