I hate to say it, but I totally agree -_-
I like the poison weapons in close combat, the additional close combat weapon and the fact that Plague Marines can have two special weapons in a squad of five Marines (plus a third in the form of a combi weapon on the Sarge). The reason why I say that I hate to agree is because I invested in putting two plasma guns in my Nurgle Marine squad and now I kind of feel stuck running them as Plagues lest I make a waste of the extra plasma gun from my bits collection :/
In my opinion this the best way to run Plague Marines: 2x Melta guns + 1x Combi-melta in a squad of five with a Rhino. For extra fun give the Sarge a melta bomb or even a Power fist! This configuration is great for hunting vehicles and is also objective-secured, plus tough to put down and mobile.
If you don't plan to specifically hunt vehicles with your Marines, I would instead go for Chaos Marines with the mark of Nurgle and an additional close combat weapon. You get to be almost as flexible even if you don't have poisoned attacks in close combat, or the option to have as many special weapons in the squad. In conclusion, my opinion is:
- Plague Marines are best left as an elite squad that could benefit from saturating a unit of five Marines with special weapons and,
- Chaos Space Marines with the Mark of Nurgle and an additional close combat weapon each is the better option for a well-rounded Troops choice.