Everything depends on the size of your system and of course on your computer power. If you can do ab initio coupled-cluster theory then your results would trend well with experimental findings. But if your system is too large and you cannot afford such calculations, then there are various DFT options that you can test. For more information, see Vijaya Keshari-J. Phys. Chem. 1995, 99, 9045-9050; Karl Jug-J. Phys. Chem. A 2003, 107, 4172-4183 and Andrea Alparone-J. Phys. Chem. A 2006, 110, 5909-5918.

Thank you for the suggestions. I will look at these references and see what all I learn.

At first glance, my molecules are much larger than the azoles and pyrroles in these papers. However, I will see what methods they found most useful for comparison with experiment and try those. I do have access to significant computing power but will need to see how these calculations scale on that machine.

T.P.M. Goumans - I do have access to ADF through a collaborator, so I will try it out - my students have done a lot of these calculations with Gaussian09 recently, so it will be good to compare ADF with G09, both the results and the computer times required -