"Least evolved" and "most evolved" is problematic to define, though.  Patellogastropod limpets and pulmonate landsnails by definition have had an equal amount of time to evolve since they split from a common ancestor.  The limpets and the landsnails changed in different ways; one changed some things more and the other changed other things more.  So it does actually boil down to the order selected by someone.  In the case of gastropods, the modern sequence is largely following Thiele, plus all the changes due to findings indicating that particular groups are more or less closely related than Thiele thought.