IMHO it partly depends on both the airline and the airport and not just the day of the week. We just got back from Orlando and had flown out on a Sunday morning which was great in terms of no traffic to the airport but we flew Spirit which in Detroit is in a smaller separate terminal than Northwest (which has its own) and since a lot of their morning flights left around the same time as ours - we ended up having to get escorted through security to make our flight. We got at the airport at about 6:15a with a flight leaving at 7:40a and it took us an hour to check in and another 20 mins to clear security. We were literally the last people on the plane which greatly disappointed the gentleman in our row who not only realized he was not getting a row to himself but that he had the two of us and a lap baby! This fall we're flying NW to Savannah but they have their own dedicated terminal with plenty of kiosks and security so I'm not as worried.
If these aren't issues for you then I would say that Sunday and Friday would be the least hectic with Saturday and then Monday after that. I would avoid Monday just b/c you'll encounter a lot of business travellers at the airport flying to clients. Sunday would probably be the best day since a lot of people fly Saturdays to get in the Saturday night stay. Usually on a Friday a lot of business travellers may have flown home Thursday night (at least that's what happened at my former company where everyone flew) so you wouldn't be dealing with as many people at the airport but still traffic on the roads.
We were thinking of maybe leaving on a Wednesday or a Thursday and then coming back on Saturday of the next week, so like 8 or 9 nights. So maybe that isn't such a great idea? We always leave in the morning and we usually fly Delta (sky miles). Any other suggestions?
That sounds good! I wouldn't let the crowds scare you. As long as your not flying during Spring Break or holidays, it'll be fine. Just expect to deal with families on your trip back.