In general important things for choosing a good software development company are:
– using all the most modern tech innovations by the certain one
– qualified tech expertise
– finding the one with the same size as yours for more productive general work (it's a common and effective rule for business)
– checking the reviews from other people before making a choice (it’s a top tip in fact!)
– choosing a not too cheap one because they usually provide a low-quality work and you'll anyway pay more in the end
And according to many serious software resources the best companies in this sphere are Intellectsoft, Radixweb, Idap https://idapgroup.com/about-us/, Eleks, Sphinx Solutions, Apriorit and XSolve.