For me ... i choose them both because they are with the same action characters...like being action masters to "karate"...
They are in different niches. For overall action with many ingredients (like action stunts, comedy) that cater to mass audience, it is Jackie Chan. For martial arts/ fight action movies, then it is Jet Li. Though best martial arts action hero is still Bruce Lee- still unparalled almost 40 years after his death
To my opinion they are not comparable actors at all. Jackie Chan is a martial expert, but Jet Li wants to be a good actor, but not an action hero.
Difficult to compare because they paly in different genres of movies. Chan is funny, fighting skill looking similar for me, but Jet lee is more impressing and handsome.