It has to be hung loose, not nailed tight
A vinyl panel expands and contracts with temperature — noticeably, along its length, every day. It is designed to hang on the nail rather than be pinned by it, which means the nail head sits slightly proud and the panel slides behind it.
Nail it tight and the panel has nowhere to go, so it buckles in the first hot week and stays buckled. Wavy vinyl on a wall is almost never a bad product. It is a crew that drove the nails home.
The wall behind it does the work
Vinyl is a rain screen, not a seal. Water gets behind it by design and has to drain out, which makes the weather-resistant barrier, the flashing and the condition of the sheathing more important than the panel you chose.
That is why we take the old siding off rather than going over it. Going over hides whatever is rotting underneath and adds a second layer for water to sit between.
Insulated vinyl, and when it is worth it
Insulated panels have foam bonded to the back. They are stiffer, so they look flatter on the wall and sound less hollow, and they add a modest amount of R-value.
The honest version: buy it for the flatness and the rigidity, not for the energy saving. If someone is selling insulated vinyl mainly on heating bills, ask them for the number in writing.
Colour, and the repair problem
Darker colours hold heat and fade faster, and a south or west elevation ages ahead of the rest of the house. Modern formulations are far better than they were, but the sunny wall is still the one that shows age first.
Matching matters later. Profiles and colours get discontinued, so a partial repair on a ten-year-old wall often cannot be matched exactly. We will tell you when a patch is going to be visible rather than doing it and letting you find out.