Chance to stick a debuff on a target depends on several factors.
If we want to simplify it we could say that your "final accuracy" depends on the sum of the following aspects:
1) Your singing skill + your skill with the currently used instrument (Wind for flutes, String for harps)
2) Your CHR
3) Your Magic Accuracy
So you kinda have to evaluate all of these aspects when you want to decide which piece is going to be better than what.
You can't compare them 1:1 sadly, or it would be much easier.
So what you need is the different ratio so you can compare one stat to another.
1) Skills => Singing is the most valuable, it works on everything. Wind and String can be situationally very useful but you need to pay attention. Majority of time you'll be casting songs with a Flute (Wind skill) instrument, but there might be situations where you want to use a String one, for instance to increase the range of Horde Lullaby. In such a situation an item with +wind skill would be worthless. Vice-versa or items with +string skill.
Furthermore, afaik skill converts to macc 1:1 up to level ~200 (I think?) but past that each point of skill is roughly 0.9 macc. (please someone correct me!)
2) Your CHR gets compared to your target's CHR. According to this, you get an increase chance to stick your song. I never saw very detailed tests on this thing, but from very old posts and from my own and other players experiences, I always go the impression that the lowest your CHR was compared to your target's, the more 1 additional point of CHR mattered. In such a situation possibly worth even more than 1 Macc. Vice-versa, the higher you go above your target's CHR, the lower impact an additional point of CHR will have (i.e. less worth than 1 point of macc). This is not confirmed 100%, just my personal experience.
It has to be said though that first: all post-SoA items have CHR in one form or another (almost), second: you will hardly find post-SoA targets where your CHR will be higher than the target's (on targets that matter, of course), so I think CHR will always be pretty valuable
3) Macc is very linear. It doesn't have the "dynamic" worth of CHR and Skills, so it's certainly the most reliable stat to be aiming for. In spite of this, I still feel that CHR cannot be completely ignored or underestimated.
These are just my two cents, hope someone will be able to fix my errors.
Oh! Last but not least, for your legs slot I'd get Bihu Cannions. Inventory saver and awesome piece for several situations (increased SV duration, decent TP items, nice for PDT, nice for Mordant Rime and arguably best item for debuffs atm)