First, and foremost, "best" is really subjective as there are a lot of very different builds out there. If you're having fun, and progressing the game at a reasonable pace, than you're build is solid.
Before given a detailed suggestion, there's a few general questions about what build type you want, those answers guide a lot of fine points of a build.
Warrior Shield Build:
1) Are you using a STR or AGL build (1-Hand or light weapons):
There are some solid AGL builds out there (Flurry is your friend) but most Shield Warriors lean towards 1-H weapon use, which means a STR build. Increases damage and HP. NOTE: The stun immunity and critical hit reducing skill Infantry Training is only effective with a 1-H weapon, not a light weapon.
2) Active or Passive Skills:
Passive skills are used all the time, active skills give a higher benefit when used but will get used a lot less than passive skills. Active skills can also help the player feel more involved in the game. Most players use a mix, but there are some solid reasons to focus only on passive skills.
3) Guild:
Not shockingly, most warriors of any build choose the Warrior's Guild, but there are some --small-- benefits for choosing another guild.
4) Companion:
Hirge, build as a healer, is a highly recommended companion for a warrior but Gressenda can give out some nasty damage.
5) Trait Point Allotments:
I'm lumping quest trait checks and balance between mental and physical traits into one topic here. Some quests have trait checks you need to pass to get certain outcomes. Some players prefer a highly combat orientated character (strong as an ox, dump as a rock, etc). Some players prefer a balance (toss some points to PERS, AWA and INT, it pays dividends... sometimes).
6) Skills:
Questions 1 through 5 might impact on what skills you can, or are strongly advised to get, but if there's any skill you ---must--- have as a player, than you might need to take that into consideration when allotting trait points, picking guilds, etc.