It is much better to have a well organised beneficiary as the executor. I am sure that some solicitors have handled their execution duties efficiently, but there have been many cases where they seemed to lose interest and take ages. There was a case on Prime Time where a solcitor was reprimanded by the Law Society for taking years to pass on the funds.
You may need a solicitor for advice when acting as executor, but if they are slow to deal with it, then you can go elsewhere. I assume that you can't change an executor very easily
Brendan