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
"They say the test of literary power is whether a man can write an inscription. I say, 'Can he name a kitten?'" -- Samuel Butler