Only thing I would say domestically if you are doing mrs w/ 2 different a/lines, know your terminal maps in regards to the physical distance and layout from one terminal to the other. Doing a bktobk mr on UA/AA into LAX, its better to go in on AA than UA, as the a/port traffic flow gos that way. On tight connections if you flew in on UA, you'd probably have to run back-probably over a 1/4 mile to reach AA terminals. The shuttles ahve to go all the way around. Same scennario @ DFW if you connect DL from AA. Stupid underground train goes only oneway, unlike Houstons IAH. Just my 2 cnts worth.