Fibre is king hands down!

Is the phone over the HFC or is it a conventional landline?

A lot of the aerial infrastructure for HFC is in a pretty questionable state. I would be going outside and looking at the incoming cable, and where it hits the pole and house. Have the strain relief things come off their hooks, so the cable is hanging by a cable tie or staple? Tree rubbing through the line? Damage to the grey HFC termination box on the house?

SomeoneSomewhere:

Is the phone over the HFC or is it a conventional landline?

A lot of the aerial infrastructure for HFC is in a pretty questionable state. I would be going outside and looking at the incoming cable, and where it hits the pole and house. Have the strain relief things come off their hooks, so the cable is hanging by a cable tie or staple? Tree rubbing through the line? Damage to the grey HFC termination box on the house?

Eva888: ..lines in for satellite etc.

A line for satellite? Okay, that's a new one.

Seriously though, the legacy TCL/Vodafone cable will be black and quite thick, whereas the legacy Telecom copper line (assuming they still have theirs installed) will be much thinner.

Cable also has the grey (or black) node things on a lot of the power poles. If you have a look outside on the street you should be able to determine which is their cable line and check what the quality of it is like.

The overhead HFC cable will be a triple-siamese thing, that looks kind-of like a ribbon cable. It has three parts that can be 'unzipped': the HFC coax cable, the two-pair phone cable, and the insulated steel messenger wire. Looks vaguely like this, though I imagine it only has two pairs.

I would expect any problems to be near the overhead terminations, where the cable has to flex. 

Suggest disabling the other WiFi network. 

The problems between keyboards and chairs are normally the hardest ones to solve. 

Eva888: As I was reading this, a very non tech couple in Hataitai just called me to ask why their HFC internet was constantly cutting out including their phone and what to do. I suggested turn it all off etc but if it continues will have to arrange to speak with One NZ for them where they have me added as their contact person for One. They are on the vulnerable person register.

They have 3 Super Wi-Fi mesh units as it’s a big place but it hasn’t been that great since they were installed. I suggested mesh so they could attach a streaming box behind their older TV one of which which is at the other end of the house to the modem.

The husband has a terminal disease so their time is mostly home on the internet so really want to get this sorted for them and appreciate any suggestions. Cost of fibre would be an issue for them.

Personally Chorus needs competition - not just the Fibre retailers competing. I suppose only hope of that in future is wireless solutions (like cellular) rather than physical connection.  
  

Wireless will always have a higher proportion of bandwidth that needs to be shared and can be overloaded far, far more easily.

Yes, it's easier to setup wireless and it's probably a great solution for lower-end users but someone using near 1TB a month is hardly going to be interested in a shared bandwidth solution - they will go for the likes of fibre every single time. I certainly wouldn't look at wireless if fibre was available.