Five readily available software packages were tested on nonlinear regression test problems from the NIST Statistical Reference Datasets. None of the packages was consistently able to obtain solutions accurate to at least three digits. However, two of the packages were somewhat more reliable than the others.
Mondragon, Paul Fredrick and Borchers, Brian
"A Comparison of Nonlinear Regression Codes,"
Journal of Modern Applied Statistical Methods:
1, Article 31.
Available at: http://digitalcommons.wayne.edu/jmasm/vol4/iss1/31