Caveat: Long Read.
There is no perfect build
One beauty of PVP is the variation and customization it offers to players. With the endless possibility of different affix combinations, you will never run out of ideas/or ideas to copy 
Here are my observations of crafts with thousands of experiments and matches. I classify them into all-rounders and specialists for purposes of my discussion. All rounders can take on every other craft with varying degrees of difficulty and strategy. Specialists uhmmm…, specialize in specializing their specialized tasks. Just kidding. Specialist crafts are very good at what they do but there are certain crafts that just counter them perfectly.
ALL-ROUNDERS
Pure Immortals
-the most common in the upper divisions is strong vs. all other builds. It is the best-all rounder for AI gameplay. The downside?
Other immortals with some form of anti-immortality. Sure you can draw up to round 12 or so and see your character survive with more than 75%hp left in tank. But after so many draws, you will be surprised your opponent will actually devour you. Still, I suggest everyone to have at least one immortal craft in their inventory.
Hybrid Immortals.
This class has been unspoken of. These are the ones I am referring to above that possess some kind of anti-immortality. These crafts sacrificed some tankiness in order to get the edge vs. their own kind. They are very good all-rounders for active gameplay and their AIs are headaches to pure immortal users. You will beat immortals with minimal number of draws with this type of craft. The problem is that the AI will be easily killed by high damage crafts and other strong hybrids.
Storm Burst Rogues and Warriors
They are very good all rounders for active gameplay. High mobility allow them to do hit-and-run maneuvers against almost all builds. They have the ability to bypass immortal tankiness by stuffing in lots of deadly strikes and crits. Downside? The AI is fragile and it needs some kind of training on the part of the user to defeat strong ricochet and barrage campers.
BloodMagic Builds
These builds are hp monsters that reach up to +1.0million in the arena.
They are the original tanky build before the rise of immortals. In general, this craft deals more damage than immortals but they have less damage reduction and almost no regenerative ability. They survive barrage builds better than immortals do-I cannot think of other benefits to using them because they are rendered obsolete by the introduction of immortals.
SPECIALISTS
Barrage and (Olympian Craft)
The barrage is my personal favorite. A well made one kills anything it touches-immortals, blood magics,etc.-you name it. However, there is one problem-you cannot touch everything. You will face long ranged crafts like ricochet and other barrage crafts. There is a way you can beat other barrage crafts but the pistoleer rogues don’t want to be touched at all.
I am not the best person to discuss Olympian but the Olympian definitely has the same limitations as that of barrage crafts.
These are specialist crafts. You cannot get to no. 1 spot if you only use barrage or olympian crafts only. You must use at least one of the all-rounders. However, these craftswill take you near the top the fastest.
Ricochet Crafts
The hate craft. I hate it so much that I had to make one myself : It has the longest range in the arena and the knockback talent is really annoying for non tanky crafts. Not too long after I left it in the arena, I got chests from it despite not being finished that moment. @flasher13’s pistoleer rogue probably has thousands of rare chests now waiting for him.
Like the barrage, this is also a specialist craft. It is made for passive gameplay/camping. It can take on barrage crafts and other non-tanky builds. It cannot take on tanks, unless you use bomb to vault away from immortals until you earned enough draws to fell one.
Summoner Crafts
(Div 1. is waiting for you @dickwad…)
This is possibly the most fun craft if only they can also beat immortals 
I do not have an analysis on this one since the only summons I see are apocalypse furies.
The day of the summoner has finally arrived in the arena!!!
Sounds strange does it not. Just think of a great build or copy a great build first then just make sure you have apocalypse mythic in main hand weapon. Virtually everything from the main character transfers to the minions. Let’s suppose mythic procs do such as apocalypse. Now a fury is such a mini me of your arena toon that the chances are highly unlikely but not impossible. Also maybe cerebral cortex is passed down but highly unlikely