Abathur is many things in Heroes of the Storm; a specialist, a starcraft hero, a base afker...but most of all he is one of the most versatile heroes in the entire MOBA genre. This build is one of, I think, numerous viable builds on Abathur; its just one that I happen to have extreme success with (at least since the Kaelthas patch). This build is entirely focused on buffing Abathur's healing and single-target damage potential; making him a good support and a high damage hero while retaining zoning capabilities and Lane Presence through Evolve Monstrosity.

Level 1
Regenerative Microbes is simply the best choice for this build. It provides healing if your team has none, and extra healing if your team has some. The other talents are fairly niche in their own respective builds, be it for Locust Abathur, Trap Abathur or AOE Abathur respectively.

Level 4
Sustained Carapace is the best talent for this tier, going along with our continued buffing of Carapace. This talent is extremely important as it allows you to go from host to host passing around healing and a nice shield to everyone. Second best is Adrenal Overload, which I would only choose if the team has two supports that do high basic attack damage (i.e. Tyrande) and a ranged basic attack damage hero (such as Valla).

Level 7
This time we will be buffing Abathur's single-target damage with Needlespine. It is a fairly self-explanatory pick, given the build's objective. Networked Carapace works if you are being forced to solo a lane or on maps such as Haunted Mines, where your pushes topside could win your team the game.

Level 10
Abathur has two really good heroic abilities. However, I would almost always suggest Evolve Monstrosity because it allows Abathur to both push lanes extremely well as well as join teamfights in a more physical way if needed. Ultimate Evolution is very good if you know exactly how to play many of the heroes on your team, but I just find that it is less consistently good all around in this particular build, as you want to be a symbiote as much as possible.

Level 13
There is no need to buff our locusts and our AOE damage is not the focus here so Spatial Efficiency is the clear choice.

Level 16
This level has some pretty good talents in it (as it does with most heroes). Adrenaline Boost is my favorite due to its supportive power in teamfights, especially when paired with our level 20 talent pick ( Hivemind). Volatile Mutation is good on maps such as Haunted Mines for the same reason that Networked Carapace is, and thus these two talents often go together.

Level 20
For this build to function as it is supposed to, Hivemind is the only true option here. This ability will allow you to put shields on two heroes (healing both as well) and deal twice as much damage with successful Stab hits. Ludicrously good with this build and a must pick, the other options don't even come close.

Early Game (Levels 1-9)
This build excels more in the mid-to-late game, but early game support Abathur still packs a punch. Early game Abathur is at his best on all of the maps minus Haunted Mines. Abathur will struggle through the first mine opening, but afterward he will excel on that map as well. Standard strategy is to simply pick a lane (preferably near one of the objectives, and on the Raven Lord map be sure to move closer to the tribute location in order to drop Toxic Nest). Your job early on will be to either solo a lane or support a 2v1 lane, and defend the objective associated with your lane. On maps such as Dragonshire, place your Toxic Nest near the enemy side of the capture point and the two patches of grass leading into the top/bottom lane in order to keep your team abreast of the situation at that objective. This strategy works on most maps, and will make your team happy that you have your "eyes on the prize" so to speak.

Mid Game (Levels 10-16)
This is when Support Abathur comes into his own. Once you have Evolve Monstrosity, its time to summon it down an unattended lane and then focus your attention on teamfights. If no teamfights/objectives are up, focus on pushing the lane your monstrosity is in, being sure to use Carapace on it as often as possible to keep it healthy. During teamfights, Symbiote the team initiator first, and place a Carapace shield on it. Pop your Stabs and Spike Burst and then immediately Symbiote onto one of the damage dealers on your team that needs the healing and shielding powers of Carapace the most. As an aside to this part of the guide, I would ALWAYS suggest using Quickcasting with Abathur in order to maximize the speed at which you use Symbiote and Stab. If you do this, you will be surprised how quickly you can jump from host to host and how much healing and damage you will be doing.

Late Game (Levels 17-End)
Not much changes for Support Abathur in the late game, except he receives the ultra-powerful Hivemind talent at level 20. Hivemind doubles your healing and damage potential, and makes it so you don't have to shift around your Symbiote too often (unless your team spreads out a lot, in which case the Hivemind will drop off and you will need to find a new host, likely). Alongside the constant lane pressure provided by your Evolve Monstrosity and the teamfights you are supporting heavily, victory comes fairly easily in the late game, or so I've found.

This was my first guide, and I decided to create it just to show an example of an Abathur build focused more on supporting teamfights than anything else. I have found great success with this Abathur build in solo and group-queue quick match as well as Hero League. I hope others find it as good a build as I did, and I'll see you in the Nexus!

Note: I will add/change the guide as needed with additional playtesting and any comments I receive.