Not true as far as Trane/AmStd aluminum coils. In fact that is the way the market is moving. Carrier and others had copper coils which were prone to leaks. They have moved toward tin plated and now aluminum.

You don't mention size but of the three listed AS Allegiance 13 with best matching evap coil would be my selection.

IMO

Thanks for the advice.

all sizes are 3 tons as old one and 13 seers, though carrier gave me other options (performance line but minimum is performace-16, it seems performance line doesn't have 13 seers.)

Only one contractor said I should replace my lineset, existing line is 3/4, new one will be 7/8. However, it's not easy to replace from attic. Does flushing the old lineset work OK?

Important that lineset be sized to manufacturer specs.

IMO

I have 2 air conditioners from Goodman. They make some great air conditioners. Energy efficient, quiet, remote and neat functions like auto on and off after the room cools down but most of all they are reliable. One of my first purchase out of high school was an air conditioner from Sharp and it has ran the same as it did 8 years ago.

Cant add much but my advise...
-Look out for Goodman air conditioners as they make some of the best
-Bigger is not always better but still at least get a 8,000 BTU as your room cant be that small
-Make sure it has on and off fictions or "energy saver"

Here is a link that might be useful: 13 SEER Air Conditioners