When it comes to War, there are a few sub jobs you should have in mind. Honestly, almost any job can be a sub job in the right situation. However, when it comes to the basic uses of Warrior as applied to partying or missions or anything of that sort, there are a few you will usually select from.

Monk: No doubt if War is your first job to 30, this will be the sub you use. Honestly, it's not too bad of a support job beyond 30 neither if you plan to use Great-Axe. However, most parties have pre-conceived notions, so be prepared for them to ask for Ninja even with the two-hander update. Usually though this job loses it's luster in parties beyond 24 as Utsusemi is a nice additive if you have to tank, or help tank.

Thief: This is another two-hander sub. Usually this is used when you're looking for a boost of WS dmg with your two-hander in a notorious monster setting. If you have your War in sky, look to this job to be your best friend for SATA Steel Cyclone.

Samurai: Honestly, this sub is pretty nice and useful when you're trying to solo with a two-hander. Third Eye + Seigan is nice, though obviously not as dependable as Utsusemi would be. Meditate is also a nice little perk to this sub, aside Hasso of course. Honestly though, this is not a sub I use very often. As a War75, the only time I really used this sub was to fight Kirin, and only because it was a quick 60tp when your accuracy sucks and a nice 300tp if you're sitting on the sidelines.

Ninja: Obviously if you've been playing FFXI for long, you know that Ninja is the primary sub for Warrior. This is the sub I use most, and the sub you'll find most often in an exp party. However, don't let yourself be fooled by other wars when using this sub. It is not always necessary to dual axes. Finding a nice axe to main hand, and a sword for the off hand is very do-able. Some swords have much better stats to add on like Acc or Att. And of course, the shadows are nice and reliable until an aga comes along. But if you ever consider War as a job beyond 24, this sub is in your best interest to look to.