If their airfares go lower you can get credit on future flights for the difference, also they are much more flexible on giving you airfare credit if something happens and you have to cancel your flight than most airfares. Be sure and read the fine print on both of these as well.
As others have mentioned check out United’s baggage policy, because I recently compared them for a flight for dh and while United’s tickets were cheaper the luggage cost made them considerably higher. I may be wrong, but I believe they were the airline that even charged you for your carryon luggage.
Also, wait on purchasing your tickets until closer to time because SW’s deals are generally not very far out from a travel date. If you can fly on Tuesday-Thursday do so. It will be cheaper than weekend travel.
You might also want to check on shipping your luggage via UPS if you are flying with a carrier that charges by the bag and you either has a family member that can accept the packages or the hotel will. Then only take what you absolutely need with you to the airport. I know a lot of people do this for trips to Walt Disney World to cut costs.