We have Comcast and bought a Motorola SBG6580. Probably cheaper in the long run over leasing but it's kind of a pile of crap (modem is OK, router and WAP are junk) and when you call for service it's always because of /your/ modem. So in that sense leasing the modem means if you've got a connection problem then you play dumb and blame Comcast.
'91 Toyota Pickup
'09 Kawasaki KLR650
'12 Gunnar Rockhound 29
"To live is to suffer, to survive is to find some meaning in the suffering." -- Friedrich Nietzsche