The easiest and most comfortable trip is LAN via LIM. You get a lie flat seat the entire way, you have an easy LIM connection (a quick security re-check and a quick gate check on the US-bound flight), you get to arrive SFO on your return home early AM and only have SFO Immigration to deal with - you don't need to deal with another airport, then TSA, etc etc. The domestic narrow-body experience with most other airlines to get to the point of your int'l departure (especially on the return, when you just want to lie down the whole way) rules out all of the US carriers on the route, and even AC, which has a decent front cabin product (but there's a SCL stop, so it is SFO/YYZ (narrowbody) SCL/EZE.)

Mid-Dec to Jan is going to have horrible pricing at this point.