Dagger or Ridill offhand, TP gain amounts to about the same if you're using Triple Attack merits and Assassin's Poulaines. Personally I prefer dagger because I see better results when I have the flexibility of using 2 daggers instead of Ridill. Sooner or later, Ridill THFs are going to have to face the reality that there's just a limit to how much you can get out of Ridill on LV75 things.
Whoever said THF/WAR or THF/SAM is more viable than THF/NIN needs his head examined. THF/WAR has a respectable damage increase but you take a huge hit in flexibility and TP building. THF/SAM is fine when you're just sitting on your ass with nothing to do during a fight, but you're gonna take a sizable damage and TP hit for it.
I use 2 sets of gear and that's all I really need to perform just fine when it comes to xp PTs. Dagger+12, Crit Hit+3%, DEX+2 in meripo.
Weapons (main, sub, ranged)
-Martial Knife / Blau Dolch (jury is still out on Blau vs Martial)
-Thief's Knife / Daylight Dagger / Heart Snatcher (varies)
-Lightning Bow +1 / Ungur Boomerang
TP Gear:
-Optical Hat
-Specs
-Suppanomimi
-Merman's Earring
-Scorpion Harness
-War Gloves +1
-Sniper's Ring
-Rajas Ring
-Forager's Mantle
-Life Belt
-Hecatomb Subligar (there's no real substitute for it that comes close)
-Assassin's Poulaines
WS Gear:
-Hecatomb Cap (no real substitutes available)
-Spike Necklace
-Pixie Earring (Merman's Earring would be ok substitute)
-Merman's Earring
-Dragon Harness +1 (Hecatomb Harness is decent substitute)
-Hecatomb Mittens +1
-Spinel Ring
-Rajas Ring
-Forager's Mantle
-Warwolf Belt
-Hecatomb Subligar
-Hecatomb Leggings
XI Wiki

