Regarding your question for the landing flap: I'd say 90% of the time I use F30, instead of F40, on the 737...F40 gives you a little lower Vref, but a lot less margin to run into the flap overspeed (175kn vs 162kn; GUSTS!). Additionally the airplane is, in my opinion, nicer to fly with F30. Nonetheless, if operationally required d/t landing distance, steep approach, contaminated runway etc F40 is used. I don't think there's a huge economic impact on using F40 instead of F30: Flaps come out very late so fuel burn isn't really an issue, maybe less wear on the brakes...
For the A/T: I guess it really depends on the type of the airplane - Airbus logic in general is to leave A/T in till 20(?) ft, when the ship tells you to retard (SOPs can be different though,
AFAIK LH group does it differently). Boeing's logic is different and all over the place. for example the T7 cancels A/T only when selecting reversers, while the 737's A/T system works acc FCTM in a way of AP off = A/T off (Even though you could leave either engaged, with the other off). Yet I know of a few guys keeping it armed on approach (not engaged, just armed) for low speed protection. Personal preference and/or SOPs I guess.