New stuff, quite often the reason for poor shifts is something being slightly bent, pivots being worn, cables stretched or worn, outers being worn.
replacing cables normally improves my shifting when no amount of tinkering can get it right.
In terms of preference I prefer down shift (to the larger sproket). As a general rule I am more likely to down shift under load while pedalling so don’t want dodgy shifing. If you are shifting up I’m normally going faster or accelerating so can lighten the load on the pedals for the shift.
Having said that up shift is more affected by worn components as it relies on the spring to pull the mech back down so any sticky pivots or cables have an impact. Shifting down you just notice it getting a bit heavier and can compensate.