lol @ SAM/NIN.
Seriously, the obsession with /NIN has got to stop at some point. Hasso and Seigan increase the recast timers by 50%, so unless there are attacks you absolutely must avoid (such as magic or the poison effect from those Lamia in the ToAU missions) Seigan + Third Eye will do just fine.
The above posters pretty well covered everything on SAM/WAR, but I'm going to have to seriously argue against Ifrit's priority list.
Now that 1 STR = 1 Attack and 1 DEX = 1 Accuracy, atk and acc gear take a back seat to STR and DEX (especially STR at 60+) unless you're getting a significant boost (such as the +20 from Ochuido's Kote).
The reason for this is because all Great Katana weaponskills use STR as their stat modifier. This on top of STR generally increasing physical damage output allows SAM to pile it on for great effect. It's especially noticeable at 60+ when you start to get the last 3 WS you will ever use; Tachi Yukikaze, Gekko, and Kasha.
These 3 WS have a STR modifier of 75%. That means for every 3/4 STR, 3 DMG is being added into the equation (on top of the other benefits of high STR). This makes for some killer WS.
The last two points I want to make are you should generally be eating meat full-time now since your DEX bonus is now good enough to forgo eating sushi (unless for some reason you're over hunting and the mob is just impossible to hit) and if you haven't already, get cracking on CoP missions.
At level 50, if you're on or past the mission you fight Ouryu (4-2 I think?) you'll have access to an area called Cape Riverne #B01. In this area is a ??? where you can trade a Cluster Core to spawn an NM Cluster (3 Bombs as a single mob).
You'll need at least 10 people to take this guy down, and at least 2 people who can reliably stun it to prevent it from using Self-Destruct. If you beat it, there's a good chance it'll drop the
Soboro Sukehiro.
This is one of the best weapons a SAM can use (except on thief sub; never ever use it on THF sub because of the low base damage) and it will last you all the way to 75. Before the recent patch, Soboro was at least on par with
Hagun. Now (at least in merits) it can easily beat it due to the increased performance from the update and the insane number of weapon skills you can get off per fight (You should easily manage at least 4 if not 6 or 7 a fight)
That's all for now, enjoy SAM and get THF RNG and possibly DRG leveled up as well since they're also pretty cool subs for SAM.