Starting warrior, need some advice!

[Mathieu]

SAM sub will work from Lv1 to Lv99. DNC is sometimes used to help at lower level parties, but I can't at all recommend it past Lv50.

Samurai really doesn't work very well at lower levels. The skills people sub Samurai for don't really come into play until level 50 and 60. Store TP, Third Eye, and Zanshin help, but they are weak compared to what other subjobs offer at those levels.

If you want an easy subjob for those early levels, go with Monk. It's a whole lot more effective than Samurai up until Samurai starts giving its better toys. Monk also is very easy to level up and doesn't cost much.

Until about level 50 or so, use Shield Break.

Sturmwind is nice if you want to clear that last chunk of HP the mob has to end the fight, but more than 95% of the time, you'll likely be wanting to use Shield Break. An effective +40 Accuracy is nothing to scoff at, particularly in the early levels.

I'm going to have to disagree with you. Once you have Sturmwind, Shield Break is a niche weapon skill that it likely only going to be used when doing level capped quests or when you get into higher level content. Shield Break just doesn't help since 95% of the time to when leveling up, you are going to hit nearly 100% of the time without it.

If you are in a situation where misses are occurring frequently, Shield Break should be your go to weapon skill. However, those situations no longer are as common. You definitely don't want to spam it against enemies that you can hit easily. The damage difference between Shield Break and Sturmwind is too huge to use Shield Break as a "just in case" weapon skill.

Back before they revamped pretty much everything, Shield Break was a lot more important in early levels. However, between rebalances and increasing experience on low level enemies so IT weren't the only viable leveling mobs, a lot of the reason why Shield Break beat Sturmwind no longer exist.

[Arcon]

Samurai really doesn't work very well at lower levels. The skills people sub Samurai for don't really come into play until level 50 and 60. Store TP, Third Eye, and Zanshin help, but they are weak compared to what other subjobs offer at those levels.

Not many jobs matter at lower levels at all. MNK and DRK are both better DD options than SAM at lower levels, but personally I don't think it warrants leveling either of them up before you have will switch to SAM for higher levels anyway. The rate at which you gain EXP is too fast that worrying about miniscule damage upgrades during that time is worth it. But I guess it depends on what you wanna play like. If you wanna be the best you can be at any time, then go for MNK at first, switch to DRK at Lv30, then to SAM at 50.