I have to chime in here, I had AT+T and the speed was so-so, went down a few times while I had it.
My parents got Optimum OnLine a few months back, its very, very fast, seems not to be capped at all.
Ive done the speedguide tests at several different times of day, all seemed exceptionally well and fast.
I think it relates to the service being new to the area my parents lived in, (Watertown, CT) cable net access was just announced about 2 weeks before they got it, myabe its not overloaded yet.
Myself, I had Adelphia Powerlink cable net access, service was so-so, went down about 3x the 4 months I had it, email was down quite alot, then the @Home stuff happened and my service went downhill, supposedly Adelphia isnt run on @Home (from what they say) but the service was total BS now.
I called and talked to the tech people several times, they said theres no speed problems at this time each time I called, they said to check my PC because there was something wrong, I tried with/without router (Linksys), 3com, Linksys, Intel, generic nic cards, different cables, etc, same slow problem.
I signed up for DSL form SNET (to be turned on 12/27 but already on and running since 12/16) and did side by side tests from the same speedguide test site at 1130pm on a Sunday night (shouldnt be primetime should it?).
Cable = 26kbps down, 86kbps up (best result out of 4x)
DSL = 980kbps down, 109kbps up (best result out of 4x)
For me DSL is better, fo rmy parents cable is better