For your parents, CLE is the obvious choice, as everyone above noted.

However, for a mile-hungry elite like myself, EWR is the choice b/c it nets more miles. If I go IAH-CLE-PA or other places on the east, I'll get 1091 for leg 1, plus whatever for leg 2 (usually 500). For IAH-EWR-East, I'll get 1415 + the second leg. Sure, the 324 miles isn't a lot, but it adds up... and I have a great friend in EWR. If I ever mis-connect, I have somewhere to stay and get a meal with