@marciosmg
Well, it depends on many factors.
First, what is your highest stat, Intelligence/Magic or Faith? Firestorm needs 3 slots to be equipped (18 intelligence) and God's Wrath needs 2 slots (16 Faith)
Secondly, Firestorm acts like an eruption of constant Fire Damage around you, but it isn't even. There are spaces between the flames that your enemies can use to attack you if you're not careful, but if you set up the spell properly, it does some really high damage (300 - 400 damage to the Red Eyes soldiers in 1-4, it's damage calculation is each 10 levels of magic adds 285-340 Fire DPS)
God's Wrath on the other hand, works like an expansive force aura around your character, dealing pure magic damage, and pushing your enemies for quite some distance. It has a longer range than Firestorm and there are no spaces nor weakness that the enemies can exploit, but the damage is significantly lower (150-200 Red Eyes in 1-4, it's damage calculation is 100*Faith Level)
Current PC Build
CPU - i7 8700K 3.7 GHz (4.7 GHz turbo) 6 cores OC'd to 5.2 GHz with Watercooling (Hydro Series H110i) | MB - Gigabyte Z370 HD3P ATX | Gigabyte GTX 1080ti Gaming OC BLACK 11G (1657 MHz Boost Core / 11010 MHz Memory) | RAM - Corsair DIMM 32GB DDR4, 2400 MHz | PSU - Corsair CX650M (80+ Bronze) 650W | Audio - Asus Essence STX II 7.1 | Monitor - Samsung U28E590D 4K UHD, Freesync, 1 ms, 60 Hz, 28"
