Hi Limlim,

I do not know what field or application you have but if it is for elisa analysis, MasterPlex ReaderFit will be a good fit (no pun intended). It has a Best Fit feature which optimizes based on 3 parameters that you can choose from: root mean square error, r-square, or standard deviation of percent recovery. It is extremely user friendly and you will find the learning curve to be minimal. There is a fully-functional 14-day free trial and a short demo movie if you are interested:

http://www.miraibio.com/masterplex-readerfit/curve-fitting-for-plate-readers.html