If you travel in WT/WT+: yes it is. If you travel in CW/F no it isn't but you'll probably get one anyways simply because you fly in CW/F (if more than twice a year that is).
It all depends why you are in the program. If you are looking for free upgrades domestically and better redemption rates, pick AA. There is not much value that BA Silver has over AA except for the lounge access on Domestic flights. Become an Admirals Club member and that is sorted, right?