As you don't mention what kind of problem you ran into with Mathematica, it is difficult to give you precise advice. I often use the Matlab Curve Fitting Toolbox for data fitting, with very satisfying results and ease of use.

I used BestFit. It is easy to use and provides really interesting outputs. It does have only 30 days free trial.....all the features are on until it expires.

Regards

Dear Saba Noor,

I recommend function 'fitdistr' of package 'MASS', one of the standard package of the R system. This function fits the given data to a user-defined standard univariate function using Maximum likelihood. R is free software so you can download it from CRAN.

Hope it helps.

Augusto

MATLAB has a lot of tools for fitting models to data:

https://de.mathworks.com/discovery/data-fitting.html

Mathematica isn't the easiest program to use, and neither is MatLab. Perhaps you'd like something with less options and more focused into curve fitting. There are many options, although most of the best ones (i.e., Origin, Graphpad Prism, Igor) are not free. I would recommend you Biokin's DynaFit. It's free (for academia), VERY powerful, and easy to use. Plus, it does not require you to know the explicit equation for your model, but uses numerical approach to find the best fit. 

http://www.biokin.com/dynafit/

Dear Saba Noor,

I recommend to use Microsoft Office Excel trendline, you can choose any one of these six different trend or regression types: linear trendlines, logarithmic trendlines, polynomial trendlines, power trendlines, exponential trendlines, or moving average trendlines. The type of data that you have determines the type of trendline that you should use. A trendline is most accurate when its R-squared value is at or near 1. When you fit a trendline to your data, Excel automatically calculates its R-squared value. you can display this value and equation on your chart.

see "https://support.office.com/en-us/article/Add-change-or-remove-a-trendline-in-a-chart-fa59f86c-5852-4b68-a6d4-901a745842ad" for more information.

Dear Saba, for me Mathematica is a good tool for fitting data, but there is not a general rule or method, every single model must be analyzed using specific fitting functions. I have found that Mathematica Application "Experimental Data Analyst" (a thirdy part software based on Mathematica environment) is very good for fitting data (see link). Do you already know this package? Gianluca

https://www.wolfram.com/products/applications/eda/

Oracle - Crystal Ball. but it only has 15 days trial. I need to use it a lot and it is too expensive; so, i got another laptop just for this. After the 15 day trail, reinstall everything ;) it is a bit painful, but time management is important.

Gianluca- to utilize "Experimental Data Analyst" , from where I could upload EDA.zip file