So intelligence magic is like your missile spells, generally with a medium range when compared to a bow. There’s crystal versions of most of them, and then some support spells with magic weapons to summon temporarily, defensive buffs, and a few ways to buff weapons with an effect.
Faith focuses more on healing, short range attacks, and fire. It’s got some pretty cool attacks like triple discs and huge fireballs, although I feel like fire spells also have more overlap with intelligence than the prior dark souls games.
Each one also has a different set of weapons to scale with. For me Faith has a much cooler roster of unique weapons, which tend to be a little heavier and slower using strength as a secondary stat, where intelligence tends to mix better with dexterity a little more. This is all pretty general, I suggest booting up your old character and digging through extra weapons to see what you might want to build towards.
I played through both ways, and hands down intelligence build is super powerful in PvE and has a certain combo that basically acts like the “I win” button. Faith was more fun to me though, if a bit more challenging. I had a lot of fun stomping enemies with the magma swords, and in PvP the winged scythe can really surprise people (special move blocks use of healing flask).
Remember you can always go to Renalla and respec too, so you can experiment a little before committing to a build. I ended up doing this just so I could cast all the spells a few times and see how they work.
For me dex is my overall go to, so I will probably try to cruise with that and stay as low level as I can while making my way to the DLC. Then I will likely rebuild around any cool weapons or spells I find, so Renalla is a main stop on the way to ensure I can respec as needed. I don’t like respeccing a lot but its hard to plan when I don’t know what I will find first in the new content, so I can give myself a pass on this one. Similarly with the spells, I think I will try Arcane stuff out since I havent done much with that (this seems like bleed, curse/debuffs), and that may change when I find DLC content too.