I think one of the best quality and functioning calculator ever I used is Casio 991MS. In that I got 401 functions used for different purposes. And I am using this calculator from long time and never got complaint of repairing the calculator. It is little bit costly but also very good and effective calculator because it has all tnctions which we have to use in the life.
It works very fast calculations and also has memory function, Repeat/Reply function which enable us to check the calculations we done. So Overall I will give this calculator 10/10 as per my use and experience with this calculator.
I will definately say it is cost effective and must use calculator for each and every calculation. And majority of professionals use this calculator for calculations. And It is little bit Complicated to use but not so difficult. Everybody can learn by reading manual which comes along with it.