Either of your plans will work. Both good.
For Southern regions of Chile and Argentina, November to March generally have the best weather ... but it can still rain and wind can blow like a Banshee!

During this same time period ... going a bit North and into central or East coast of Argentina, you can run into extreme HEAT. Buenos Aires can be 35C or higher. Go further North and it gets even hotter. Once North of Mendoza it can be over 40C. (around Salta)

Coastal Chile and the Andes are cooler, even in Summer (November to March).
By March temps can begin to cool and Patagonia and Tierra del Fuego may become too cool to ride. But further North it should cool off, with luck you'll find pleasant weather.

With Climate Change (Global Warming) it's now impossible to predict how your year will go. It's now really variable .... and crazy.

We're seeing unprecedented record breaking HEAT, COLD, RAIN, SNOW.
So we can't 100% count on anything. "Seasons" are no longer as predictable as they once were. With any luck you'll have predictable weather and have a good ride.

But as others have said, having good versatile gear is important. I would never wear Cotton jeans of any kind, Kevlar is hype. They are HOT and sweaty when it's hot and cold and wet in bad weather.

I'd much rather have vented/mesh dirt bike riding pants (like KLIM Baja or Mojave pants) for hot weather ... and use rain over-pants for cold/wet. Same with your jacket.

Quality mesh or partial mesh jacket with quality armor. Use a light rain jacket and under layers if it's cold or wet. If hot, strip it all off and ride in the mesh dirt bike riding gear. It's wonderful in the heat! If it's over 86F ... that is the best set up, IMHO.

I've ridden in S. America and been to Ushuaia five times over 3 years. But it's been years since I was there. But I do ride in our California Sierra Nevada mountains year round. I am quite familiar with going from 4000 meter snow covered mountain passes down to below Sea Level to Death Valley with temps over 45C. I've done this for over 20 years. The above gear is seems to provide the most versatility.

I spent 6 months in Peru' and Bolivia in my travels and found weather hard to predict in the high Andes. Seems like rain can happen anytime. When the Sun comes out it is INTENSE and will FRY you without you knowing. Temps may not get HOT ... but Take Care with Sun in high Andes. If the Andes are too cold you could go lower in Altitude and head down into the Amazonas regions ... like Equitos, Bolivia or Maldonado, Peru'. Muy tropical!

A few links for some decent travel gear:

Klim Baja Pants - RevZilla



Summer Jackets - RevZilla
Men's Mesh Motorcycle Jackets - RevZilla