Since this is a very commonly asked question and terrible advice is usually given, I thought that I would make this quick guide to what you want to spend Mithril on getting yourself or setting as your RW.
*TLDR: Set your RW to Sentinel Grimoire Tyro, consider dumping your Mithril into the current Sephrioth/Red XIII Banner for Diamond Hairpin.*
**Tier One: Damage Mitigation**
>1: Tyro/Sentinel's Grimoire -> Blocks 70% of all damage.
>2: Red XIII/Diamond Hairpin -> Protectaga/Hastega
**Tier Two: Build Enablers**
>1: Celes/Soul Sabre -> Runic (Use RW on a Summoner/Mage to absorb all Magical Attacks and recharge abilities)
>1: Celcil(Paladin)/Lustrous Shield -> Taunt (Use RW on a Retaliator to absorb and counterattack all Physical Attacks)
>2: Vanille/Binding Rod -> Long AOE Armor Breakdown (Enables VIT0 with Protect/Shell)
>3: Wakka/Official Ball -> Short Armor/Mental Breakdown (Enables VIT0 with Protect/Shell)
>4: Luneth/Tyrfang -> Boost (Use RW on a Retaliator and stack with Boost ability)
**Tier Three: Mass Heal**
>1: Aeris/Guard Stick -> AOE Cure
>2: Tyro/Healing Grimoire -> AOE Cure
>2: Mystery Veil -> AOE Cure
**Tier Four: Abilities**
>1: Gold Armlet -> Protectaga
>1: Emerald Bracer -> Shellaga
>2: Kaiser Shield -> Protectaga
>2: Minotaur Plate -> Shellaga
>3: Heavy Lance -> Armor Break
>3: Mage Masher -> Magic Break
>4: Sephiroth/One Winged Angel -> Blindaga
>4: Cloud/Hardegde -> Paralyze
>4: Locke/Rising Sun -> Slowga
>4: Hawkeye -> Blind
**Tier Five: Damage**
>Anything which only does damage.
**Tier Six:**
>1: Lenna/Healing Staff -> Reverse Suicide (Just reload)
>2: Josef/Giant's Gloves -> Suicide
*Why I have chosen these rankings?*
Firstly these are for the Soul Breaks ONLY, I am not taking into account things like character gear choices and realm synergy.
**T1:** You are better off cancelling almost all enemy damage for a few turns than doing one big damage hit, you can do far more damage in those few protected turns with 5 properly set up characters than you can with one impressive damaging Soul Break. You are also not losing medals for damage taken or risking death and a reload. For this reason Sentinel Grimoire Tyro should almost always be your chosen RW (Roaming Warrior), if you have him then you can choose another T1 or T2 RW.
**T2:** Runic and Taunt can destroy single otherwise difficult bosses - but they won't always be useful like the T1 Relics are. These almost always have to be used as a RW to exploit abilities these characters don't have so don't worry about finding your own. VIT0 is controversial and will eventually stop working, these need protection to work as you'll die before unleashing 9999 hell.
**T3:** When your protection from the T1 and T2 Relics has run out, or if you took lots of weakened hits, you'll want to heal up the heavier damage you'll take under lesser protection like Power Break and Protectaga. These can count for 5 uses of Curaga, pretty awesome.
**T4:** These can free up an extra ability slot for a different ability or give you extra casts of something you are bringing anyway. The protection ones are the best, followed by the breaks and then the status effects which won't always work.
**T5:** Extra damage is nice but you are bringing damage abilities anyway, stacking multiple AOE Damage Relics and AOE abilities can beat a few fights with multiples enemies.
**T6:** You don't want your characters to die. Ever.