MT are the only providers of a proper hardware landline. Sure and Wimanx's 'phone' lines are a VOIP service, so if ever there's an internet outage, you also lose your phone service.
I have MT landline, Wimanx ADSL, and Sure mobile. Customer service is about the same for all of them. Wimanx have recently removed the ability to pay bills through their customer portal, heavily pushing you towards DD.