the newest version of symbian is the best, fastest, and most advanced. It is symbian^3, and a new update is called symbian anna. U get free firmware updates every few months at the press of a button to always keep ur device up to date.
Nokias that have this are the n8, c7, e7, c6-01, e6 and x7. The n8 is the best nokia phone of the lot but they are all quite unique so it depends on ur needs.