My limited experience of ABC iView on the Beyonwiz T series is that it's been excellent on the few times I've used it since they got it fully operational (the Beyonwiz HbbTV implementation may also have improved since the ABC first started using HbbTV).
I haven't used SBS on the T series to watch anything because, at least on the Beyonwiz Ts, the SBS HbbTV/FreeviewPlus OnDemand offering is a tiny fraction of what's available through their Web-based OnDemand. I'm not sure whether that's a limitation of the Beyonwiz or of the SBS HbbTV app/app data.
SBS OnDemand has ads, whether you view it via their Web pages or via HbbTV. You can't skip them (even, I imagine, on SKIPPA). I don't think ABC iView has ads, via the web or via HbbTV.
In Canberra, there doesn't seem to be HbbTV/FreeviewPlus available at all on Prime or WIN. It is flagged as available on SC Ten, but it doesn't work on the Beyonwiz. I suspect that's due to the lack of the appropriate DRM keys on the (open source) Beyonwiz.
I don't know whether IceTV is on board with Freeview Plus. If they are, that would give them a better chance of proper access to the Freeview Plus services. The SKIPPA is not listed as being FreeviewPlus certified on Freeview's Web pages.