Originally Posted by milepig

Unless your INTL, Delta will be T3. BA will be T5.

Several options. With immigration/customs you might be sprung at about the same time?

So, you can go to them:

Take the airport train from T3 to T5 (one stop) and meet them at the exit from Immigration. All pax come out of one of two doors and the door for their flight will be posted. There are only these two possibles routes so you can't miss them. Both exits have seats close by (sort of under the escalator) so I'd tell them to wait for you there if they arrive first.

The second option is to have them meet you at the baggage claim for your flight. ORD let's anyone into the area, and I've found this is the clearest place to meet even if you don't have checked bags. They'd need to take the train from T5 to T3 and then find their way down two levels to baggage claim (not hard, really)

If you don't want to fuss with the above, another option would be the Lobby of the airport Hilton. If you're taking the EL into the city you'll need to be in that direction in any case. From T3 you can just follow the signs to the Hilton. You'll go to the baggage claim level, down a little bit more and then you'll be on a moving sidewalk. From T5 they'll need to take the train to T3 or T2 and then follow the signs from there.

You could also meet at the entrance to the CTA station, but I don't remember any place to sit there.

Since they'll have had the longer flight and be jet lagged I'd suggest the first option, that you meet them in T5.

Finally, don't discount the option of a quick phone call. My carrier charges 99 cents a minute, so they could call you for $2.00 or less. I would think that would be worth the peace of mind. (Remind them to check with their carrier to be sure they have worldwide service, my carrier required that the option be activated.) At ORD you can make phone calls immediately after landing, but you can't use the phone within immigration/customs. I've had no problems making a quick call to say "I'm here" within that window of time.