A one-stop on DL is probably as reliable as a direct on AA. I would choose DFW as there are a lot of options to reroute you in case of IRROPs and DLs terminal at DFW is quite small and nice. I would not fear missing a connection in ATL - there will not be that long a delay. September 18 for example, there are 12 flights between ATL and BOS. DL will get you there.