How can you call an app that can only be installed in one device, "the best"? GTalk, for example, offered the same services, plus sync across all device, plus

How can you call an app that can only be installed in one device, "the best"? GTalk, for example, offered the same services, plus sync across all device, plus better security and encryption. There are and have been many messaging apps just like whatsapp: Viber, Kik... And many more that we have never heard of.