I had both in my house for a couple years. PCCW 100mbps and iCable 130mbps. Ran half of the machines on one and half on the other. My observations:
1) Speedtest showed essentially the same speed for both to local and some overseas servers.
2) Real-time usage speed was essentially the same.
3) Streaming of videos from overseas was essentially the same, maybe a slight bit more lag / buffering on iCable.
4) iCable had three breakdowns over two years, but two of these were due to repair crews in the street fixing the road and cutting a cable. One was due to equipment problem in the building. Repair teams were at the door of my place within 24 hours.
There were two other factors though which were specific to me that resulted in my dropping iCable.
iCable used a proxy-like server that spooled through various IP addresses that it showed to visiting sites. So I'd go to say cnn.com and it was say my IP address was 126.96.36.199 and then the next page my IP address would be 123.45.78.001 or something. The server was using various IP addresses (sorry, I forget the term of art here, but it was a cost-savings measure apparently).
This led to two problems:
a) my SmartDNS service could never track where I was an thus I couldn't really use it.
b) many of the IP addresses that spooled into use were on 'blacklists' as spammers, and some websites would block me from visiting due to bad behavior from some other machine that used that IP address at one time in the past.
But overall, not that big of a difference.
Hope that helps.