IPTV (well, the infrastructure for distribution) is my day job. As with all things it depends on the supplier as to the cost/quality. Traditional cable/satellite/terrestrial is often better quality, though it depends very much on the technology the IPTV provider is using.
To give you some idea, with IPTV networks it's all about reach. IE you can get more customers if you broadcast at the lowest bitrate possible, because it's then also available to those with low-speed internet connections. More subscribers means more money, so it can be a race to the bottom, IE lowest quality that consumers will put up with. So for the low end of the market you invariable end up with poor quality as a result.
For the high end of the market they use adaptive bitrate technologies which send the best possible quality based on the detected performance of your link (which changes dynamically based on other users loading it etc). This rivals and in some cases exceeds traditional networks.
Sorry, not a simple answer. I would seek reviews and base your choice on those.
