Hi Mark,
Yes I agree,selection of op amp is not easy. You should be able to identify which parameters your application should be of most interest.It could be the noise, precision or the cost for example. If your going to choose between AD845 and AD744, I would recommend AD744 where there are lots of good features compare to AD845. It is low power and has a good noise performance compare to AD845 too.I would also suggest that you simulate the device with spice model to verify the performance and suitability of the device in your application.
Phil