IMO 105, Ultegra and DA all perform very well with Ultegra being slightly better than 105 and DA slightly better than DA. Only real difference is in weight savings where 105 will be the heaviest (but still very good). I would go with brand new 105 rather than used 2 yr old Ultegra.
http://www.shimano.com/publish/conte.../105_5700.html