Nurglings are a really interesting Troops choice, this is because they're not really Troops at all. They are a little more akin to Scarabs from the Necrons Fast Attack section. This is because they're Swarms, and so don't score, making it difficult for them to be the bread and butter of an army. This doesn't mean that they aren't viable however, I actually like them as a unit, and here's why.
Whilst Bloodletters and Daemonettes give the Troops section some decent hitting ability, and Plaguebearers provide some durability and an excellent objective camper, Nurglings fill an entirely different roll, as on the field you really shouldn't think of them as Troops.
This is drifting into the realm of what makes a good Troops choice but the one edge that Troops have over, say, Elites choices is that they score. This is something that Nurglings cannot do, an therefore you cannot think of them as Troops.
Nurglings are 15pts a base, and come with 4 wounds each, albeit at T3, but still, that's under 4pts per wound. For a mere 135pts you are getting 36 wounds. That's not bad.
There are a number of ways to strip these however. The first thing to look out for is S6+ weaponry, mechdar will laugh at these guys. The second is blast weapons. As a swarm every wound that you suffer from a blast weapon is doubled. Therefore, if you see even a single Thunderfire Cannon, hide.
Despite this Nurglings still make an absolutely fantastic screen. Not only do they tie up units really well but they are also short enough in terms of models not to grant a cover save. For example, in the previous Daemons post I wrote about Pink Horrors and assault. Coupling them with Nurglings at least makes them slightly viable. They can fire over the top of them without granting their opponents cover saves most of the time, and the Nurglings are also excellent at shielding them from melee units due to their vast number of wounds and 5+ invulnerable save.
However, there is a steady balance to be stuck here. In this instance you don't really want to be spending 135pts on a meatshield, that's more than the Horror squad itself. I might be tempted to go minimal, simply because you're still a decent buffer with over 10 wounds and although you'll not tie anything up for the entire game, you'll likely hold units up long enough for your Horrors to get out of the way.
My personal favourite inclusion about the Nurglings is that they have the Infiltrate special rule. This means that they can screen further up the field, but then anything that is deploying far up will likely not want screening anyway. What I've been thinking about with this is that they can pounce on enemy backline shooters turn 2/3.
The only problem with this is that you're assuming that your opponent and their army are incapable of screening their shooty units, such as Lootas. However the vast majority of the time they are going to try and stop you from charging their long ranged, heavy firepower, infantry squads. Therefore, the way that I would make this work (as I always try to) is through target overload. Throwing so many targets at your opponent that they can't deal with them all.
This way, if your opponent decides to use their screening units to prevent your Nurglings (which will be your first wave due to the infiltration up the board) from getting into their heavy shooting, then they are likely to be unable to stop the next wave, as your Nurglings and their own screening units will tie each other up, essentially giving your Daemonettes, Fiends, Seekers, etc free reign.
In short then, although this hasn't been the longest or best spelled of posts I'm sure (no Word Processor again), Nurglings are a good choice. Despite the fact that they are a Troops choice, you cannot think of them as Troops, as they do not work as such. Therefore, when building your list keep in mind your scoring units, rather than just counting your Troops and assuming they score. I'd probably take 2 squads of Nurglings, either big or small depending upon your agenda, followed up by 1 10 man squad of Plaguebearers, and 2 squads of Daemonettes at 1,750pts.
And that concludes the Troops section. I have absolutely no idea where I'll go next, but I'm sure we'll find out either tomorrow or Monday, as I go back to Oxford tomorrow.