Is softphone better of hardphone in VOIP?

I am thinking to use logitech 250 USB Noice canc headsets for centre. Its quite easy to put it. we were using it do telemarketing and its quality was fine. Just want to know generally speaking is hard phone provide better sound quality.?

I am also thinking to switch my Voip provider coz its only supports SIP and this takes lot of bandwidth. I found there is this IAX that can be reduce that bandwith. Has anyone used this and does it reduces the quality.

I want good quality sound with less bandwidth. 1 Mbps link costs in Fiji $5000USA per month and 2m link $14000.

so I guess you guys know where I am coming from :wink: