LAX to PHL flights are the ones where they move equipment around to make sure they leave on time, and have priority over any other domestic AA flight at the PHL side. I'd definitely recommend a direct if you can. 
Flight prices are another story. Warning: it's a bit lengthy. AA uses an IBM developed booking system called SABRE (Semi-Automated Business Research Environment, for the geeky types), which was spun off from AA in 2000. In 2015, Sabre's Travelocity was sold to Expedia, and from then on required a both a SABRE license to connect to the main reservation management system, as well as IBM connector licenses. Well, if you know anything about IBM pricing: it's extremely expensive, and Sabre wasn't far behind in pricing. With this huge increase in cost, the aggregators and price adjustors mostly disconnected from Sabre in 2015 and 2016, and with it being the largest travel booking platform in the world, the rapid adjustment of airline fares ended in all of the major carriers almost immediately after.
There are now two pricing schemes used on US domestic flights: fare buckets, and demand pricing. Demand pricing is used by the LCCs that don't offer premium cabins and service, while fare buckets are used by all of the airlines with a first class cabin. With fare buckets, the prices are determined 12 months ahead with a variety of fare codes with differing restrictions (pre-purchase, no changes, and minimum stay, usually), and as you get closer to the date of departure, these buckets fill up or become unavailable due to restrictions and you are moved to the next higher fare code. You can also choose to book into a higher fare bucket if you'd like: business and government travelers frequently do this, booking directly into full priced F, J, or Y fares, which offer included checked luggage, no change fees, and so on. These range from fairly cheap to exorbitant, depending on the route, with some routes such as JFK-LAX these fares are less expensive than flying any LCC, while on others such as BOS-JFK the cost is outrageous (this all comes down to pre-deregulation pricing schemes).
One upshot of the fare buckets over the last few years is that the median price paid for leisure travel has gone down, while airlines have kept the average per seat price almost identical.
Short version: book early in a fare you're comfortable paying, the chances of the price going down later are so slim as to be nonexistent, while the chances of it going up are 100%.

Flight prices are another story. Warning: it's a bit lengthy. AA uses an IBM developed booking system called SABRE (Semi-Automated Business Research Environment, for the geeky types), which was spun off from AA in 2000. In 2015, Sabre's Travelocity was sold to Expedia, and from then on required a both a SABRE license to connect to the main reservation management system, as well as IBM connector licenses. Well, if you know anything about IBM pricing: it's extremely expensive, and Sabre wasn't far behind in pricing. With this huge increase in cost, the aggregators and price adjustors mostly disconnected from Sabre in 2015 and 2016, and with it being the largest travel booking platform in the world, the rapid adjustment of airline fares ended in all of the major carriers almost immediately after.
There are now two pricing schemes used on US domestic flights: fare buckets, and demand pricing. Demand pricing is used by the LCCs that don't offer premium cabins and service, while fare buckets are used by all of the airlines with a first class cabin. With fare buckets, the prices are determined 12 months ahead with a variety of fare codes with differing restrictions (pre-purchase, no changes, and minimum stay, usually), and as you get closer to the date of departure, these buckets fill up or become unavailable due to restrictions and you are moved to the next higher fare code. You can also choose to book into a higher fare bucket if you'd like: business and government travelers frequently do this, booking directly into full priced F, J, or Y fares, which offer included checked luggage, no change fees, and so on. These range from fairly cheap to exorbitant, depending on the route, with some routes such as JFK-LAX these fares are less expensive than flying any LCC, while on others such as BOS-JFK the cost is outrageous (this all comes down to pre-deregulation pricing schemes).
One upshot of the fare buckets over the last few years is that the median price paid for leisure travel has gone down, while airlines have kept the average per seat price almost identical.
Short version: book early in a fare you're comfortable paying, the chances of the price going down later are so slim as to be nonexistent, while the chances of it going up are 100%.