The good thing about class specs is that you can change them at any time in the game. What matters the most however is your skill on a particular spec. If you are good enough then you can perform quite well at any spec.
Warrior has 3 different specs Fury, Arms, and Protection. Both Fury and Arms are damage specs. Here are some differences that might help you decide on which spec you want.
Fury vs Arms PVP in WoW
Fury PvP
Fury spec can be very beginner-friendly mainly because of all the passive heals you are getting. You just have to do less to consistently be putting out an adequate amount of damage. Overall players have mentioned that playing fury is just more fun. Fury shines the most when you have no healers and are playing solo. The melee rotations are quite easy to master.
However, it cannot deal as much damage as arms in most scenarios. In the current situation of the game, Fury spec is just not viable. You can make it work in some cases but overall people avoid using this spec. Your skill level and gear also play an important role in deciding who wins the PvP battle. Most players recommend that if PvP is your main objective then Arms spec can be the better choice.
What Fury lacks is utility, sure it can do decent damage but has no effective defensive stance. The self-heal sometimes does not match the burst damage coming from the enemy and you end up dying instantly. But it is possible to still win fights if you get skilled enough at this spec.
Arms PvP
At this point in the game, Arms warriors are more viable in the game as compared to Fury warriors for PvP. If the ilvl and skill are the same then almost always you will see Arms come out on top. If you have a good enough healer then you can consistently deal an insane amount of damage and roll through your enemies.
However, as far as gameplay is concerned players have reported that Fury spec is far more fun. Mortal strike de-buff is a great utility that Arms spec brings to the table. One area in which this spec lacks is the self-healing aspect. But the damage more than makes up for it. Arms spec also has great mobility.
If you find yourself constantly losing PvP as an Arms warrior then it is highly likely that there is something wrong with your playstyle. Up-time is the key, you need to keep the hamstring spell up for as long as possible. Asking other top-tier players for tips on how to improve your gameplay can be very helpful.
You can play a Fury warrior if you’re doing 2s because the self-healing can help when your healer is cc’d but if you are playing 3s then you should almost always opt for Arms. Arms just bring a better toolkit to the match. If your healer is good enough you will overwhelm your enemies every time