Originally Posted by
nallison
Thanks for the response, very helpful

it does indeed seem very complicated and subject to many factors to make solid recommendations.
Just one follow up question then, if you check in as soon as it opens, where do allocations start, is it back to front, and do they allocate aisles and windows before placing people in middle seats? Thanks!
My general theory (with only short haul flights to test my theory) is that automatic seat assignment algorithms are designed to:
1) do their best for customers with elite status
2) do their worst for non-status customers, so that they are inclined to pay for a better seat assignment now or in the future
Seats are generally allocated back to front, although weight distribution requirements means that this isn't a hard rule.
If one of the back rows has an empty middle seat and the flight is going to be reasonably busy, somebody without status will be allocated to it and I don't think that time of check-in ultimately makes much difference.
The only surefire way to get an aisle or a window is to pay for it. (treat it as a small insurance premium against a truly horrible seat)
To increase your chances of an empty middle seat, then you should pay for a seat with an already allocated single traveler in it, as close to the front as you can. Therefore you know that nobody is going to come along and pay for the middle seat, and this middle seat might be informally blocked if the other passenger is elite. But when the flight is full that seat is going to be taken anyhow, and hopefully not by one-half of a couple who will then be begging for you to change seats.