boland: Compared by size, is Orcon much bigger than Slingshot?
In my opinion a smaller company should not be worse than a big company. Big companies tend to have multiple departments where each department points another department as the problem. At least, that's my opinion with telco's in NL. Calling about a problem could result being switched between several departments.
Slingshot has the option to downgrade VDSL to ADSL+ if the speed isn't high enough. That option isn't offered by Orcon, at least not explicit. And, termantion costs of Slingshot are NZD 149,- compared to NZD 199,- of Orcon.
Orcon are about half the size of slingshot by number of customers.
Quality of service depends on many factors. Smaller companies have it better for some things (flexibility, competitive desire etc) big companies have it better for other things (economies of scale, resiliency etc) so you can't really say a small company will be better than a big company or vice versa.