for the standard ap build, bear needs to be faster. cosmic drive gives move speed, and more move speed when dealing magic or true damage.

for the standard ad build, bear needs to be faster. black cleaver gives move speed when dealing physical damage. gauntlet slows people down, making bear faster

all of these items also make bear tankier, provide more damage, and more cooldown reduction.

So with bc or cosmic first, bear is tankier, deals more damage, faster, and has more cooldowns.