Both bad. For different reasons.

As usual, both, like most US Presidents are war criminals if we go by the International Definition. If you can see it objectively, which many Americans may have trouble doing so.

Bush's actions ended up killing 4+ million in the Middle East, along with the creation of ISIS. Extra ironic points since the USA gave billions to the Mujahideen, back in the day, funding a young Osama Bin Ladden, so they could wage a civil war against the Afghanistani goverment during their civil war. Because the goverment was leaning communist at the time. Seen those photos where Afghanistani women wore western clothing in the late 70's? The USA helped get rid of that by giving money to the religious zealots.

Obama murdered the most people via drone attacks in history. Mostly on Pakistan and Afghanistan at the time. Including whole families and children. Also, he pardon/freed Bushed from liability the moment he took office. If I recall.

https://www.globalresearch.ca/four-million-muslims-killed-in-us-nato-wars-should-we-call-it-genocide/5470424

https://www.theguardian.com/commentisfree/2012/jun/11/obama-drone-wars-normalisation-extrajudicial-killing

https://www.theatlantic.com/politics/archive/2016/12/president-obamas-weak-defense-of-his-record-on-drone-strikes/511454/

There are other sites that break down the fatalities of the later. Since most people ate at least aware of most of the fuck ups of the former.