For the world as a whole and the US in particular, when it is put like that it is pretty obvious: China. It has the world's largest population, largest economy in PPP terms, a rising military, expanding interests around the world, including making territorial demands on several neighbors, not to mention being a nuclear superpower as well as cyberpower, and more. Syria has a population of 22 million and an economy half the size of Puerto Rico's. It is not a major oil exporter.
However, last week it certainly looked like Syria was more important. President Trump meets with President Xi at Mar-a-Lago, and almost nothing is reported about the meeting other than some vague remarks. Important matters such as trade policy (the US has initiated an anti-dumping suit against China in steel), South China Sea issues, North Korea nuclear testing issues (US has just sent a major naval group towards the place), issues over currency management (with Trump long charging China with currency manipulation, even though it is now widely accepted that while they did it in the past the Chinese are not doing so now), climate change (where China is becoming world leader on the international policy stage while Trump claims that global warming is a "Chinese hoax"). They barely had a press conference, and what really went on in the meeting remains largely mysterious.
So, wow, much better to have the headlines and the commentaries taken up with the apparently one-shot firing of 59 Tomahawk missiles at a base in Syria, after apparently warning both the Russians and the Syrians we were going to do it, in response to a chemical attack in Syria that killed about 80 civilians, including some children. This was certainly a bad attack, but it remains unclear if it was the Syrian military or some rebel groups, although probably it was the government, and if it was the government, it is unclear if it was done by some local commander on his own or with the explicit orders of President Assad, and if the latter, was it done with the foreknowledge of their allies, the Russians, and most especially President Putin. The Russians and Iranians are claiming that the rebels did the chem weapons attacke and are denouncing the US attack. But who really knows? I sure as heck do not, and I am not sure anybody in the US government knows either, especially given the 25 reasons that have since been given for this by various administration officials.
There is also the weird matter that if it was the Syrian government, they probably did it in response to Trump declaring that we did not favor overthrowing Assad, which was previous US official policy, alhough in fact little had been done in a long time to do that, with the US effectively cooperating with the Russians and Syrians against Daesh/ISIS, if quietly and not fully.
So on the relation between this stuff and China, once Xi Jinping got home the Chinese media jumped all over Trump for the missile attack, saying almost certainly accurately that a major reason Trump did it was to distract people from all the investigations of his Russia ties. See? He is doing something Russia does not like, and Putin has announced no more cooperation on saying where planes are flying in Syria. Wow, what a great outcome. And that Xi appears not happy with Trump probably means that Trump was as unpleasant on trade to Xi in private as he was to Merkel in public, not to mention to the Mexicans. And we know Xi is not happy with this new naval maneuver with regard to North Korea. Indeed, some people think Trump did the missile attack to scare North Korea and China, although it is unclear Trump is really smart enough to think that one through. So for all the official happy talk, it looks like this very important meeting did not go well, although it is not clear that not having all those commentators praising Trump for "being presidential" while shooting off missiles in Syria would have helped on this more important matter of US-Chinese relations.
As a final point I want to remind people of something that I have seen zero commentators mention, even the astute Juan Cole who does at least note that what is going on in Syria looks like classic power politics not driven by economics. That is that the Russia-Syria alliance is a strategic and deep one. The only Russian naval base outside of Russia is at Tarsus in Syria, in Latakia Province where the ruling Alawis are dominant. It was rebel advances into that province threatening their base that led the Russians to engage in massive bombing raids to support the Assad government, and Cole does note that not using chemical weapons (which the Syrians were supposed to have gotten rid of) will mean they will bomb a lot instead, and horrible as chem weapons are, thousands of children were killed in the bombing in Aleppo. In any case, that naval base has been there since 1971 in Soviet times. This is a deep strategic relationship, and this must be kept in mind.