What is PIVX strength compared to such like Monero?
Both are good projects. Privacy-wise, I'd say they're comparable. XMR uses ring signatures whereas PIVX uses Zerocoin protocol. One big difference is that PIVX is PoS whereas XMR is PoW. Philosophically, PIVX tries for more utility as an actual currency (fast block times, fast tx speed and confirmation, and low fees), whereas XMR is more focussed on security 'at all costs'. Some other strengths of PIVX include its use of a 'see-saw' mechanism to dynamically adjust rewards between masternoders and stakers, fair community governance, and the fact that fees on the network are burned (i.e., as transactions on the network increase, the total supply will remain relatively flat and could even decrease if zPiv transactions, which are more expensive, become very common). The PIVX community is also very strong (mostly on Discord, but to a lesser extent on Reddit as well).
You can see a full comparison here: https://pivx.org/how-pivx-stacks-up-in-the-privacy-realm/
I'd also suggest checking out PIVX's current roadmap to see what other plans are in development/planning: https://pivx.org/what-is-pivx/roadmap/
Also if I'm not wrong, Monero only has private transaction, whereas PIVX has both (PIV or zPIV).
I'm personaly more interested in PIVX than XMR mostly because of PoS, because this mining thingy is getting out of hand.
One thing that bothers me and I don't understand is why is the wallet set to mint 10% od PIV to zPIV. Shouldn't that be the choice of the user exactly how much of PIV one wants to convert to zPIV?
Like a textbox where you enter the exact value of zPIV you want.