I think AA/LA via LAX is your best combo if the dates work out.

I'd say the IAH stop is probably your #2 . IAH will have a Polaris lounge open by next February (at that point construction will have been underway for nearly two years; I think it's a safe bet) and if traveling with a significant other, the sCO BF seat on the 777 is a pleasant option. I doubt any of the 777-224ER fleet will be retrofit to Polaris by then. SCL-IAH is a 763 which will either be the sCO BE Diamond seat (again, good for a couple) or the Polaris seat, which is quite private, but less of an issue on the redeye and similar to the privacy/isolation of a reverse herringbone seat.

The DL option calls for an ATL transfer which adds the most circuity to your journey in both directions, so that would be the 3rd choice IMV.