Most e-Sword modules are available as MySword modules. You can easily convert e-Sword modules to MySword, unless the e-Sword module is a commercial/premium/paid module. Those are encrypted and cannot be converted.
Most of the decision comes down to the platform--Apple iOS or Droid. Functionality seems about the same. I'm a fan of Samsung Droid phones because the screen size of the Galaxy Note's are so large. So, I use Mysword on that device. I have e-Sword HD on the iPad.
How can I convert esword modules to my sword?