For most people it is a matter of preference as much as what's the best DVD player software. It comes down to features and what you need to fulfill your movie viewing needs.
You will find thousands of sites that claim to have the best software, however in the end it comes down to the top 10. Considering that there is so much software available, the majority of which share the same features, you would think it's easy to choose one that meets your needs. It's easy in most cases to locate what you need at the moment. What about in the future however? With the constant change of file types, new formats and resolutions will what you have now hold up over time?
How frequently do you receive updates for your DVD software now, how complete are the updates that you receive? Is there a great deal of bugs, do you need to locate new codecs more frequently than you want? Keep in mind that rankings for software are frequently based on the number of sales instead of how good it is. Also you have websites just trying to push their solution making use of false, user reviews and testimonials.
When choosing DVD player software, you might want to try any free trials that are available and try multiple products. Make sure all your movies play on one player and make certain they run smooth, ensure you're not having to download a ton of data just to play a movie. Also make sure that updates for your software are free, at least until the next major version. Because of the constant change in formats you do not want to be stuck purchasing each update. Make certain that your software comes with support 24/7, search the product you're considering down on the net and see how many bad reviews it has and how many good reviews it has. Also search the net and attempt to locate every possible file type and be sure your new player supports every one of them.