Whitchurch, Rhiwbina, Lisvane, Penylan, Cyncoed, Thornhill, Llandaff and Radyr are all 'nice' areas of Cardiff. Pontcanna is v expensive but central. Llanishen, Roath, Canton and Fairwater / Danescourt and Llandaff North are middling.
Have a look at Cardiff council catchments map for exact info but for primaries, Rhiwbina has Llanishen Fach and Rhiwbeina primaries - both v good, Radyr primary likewise and Whitchurch has a new primary opened by former pupil Gareth Bale this week! Whitchurch High and Cardiff High are v good. Whitchurch excels at sports too. I think Radyr High is also good. Llanishen High seems more mixed.
Estyn is Wales equivalent of Ofsted so check their inspection reports.
Have assumed you want state, English medium schools in my reply but there's also private and Welsh medium of course.
We relocated here from London two years ago but are still at the pre-school stage. Happy to help!
I find mumsnet quiet in terms of Cardiff mums tbh but there are a few active Facebook groups. Cardiff is great for kids and families!
Where will you and your husband be working as transport is a consideration too of course.