As someone who's painted over 100 plague marines, I've come to the conclusion that this is my favourite model of the lot. Since it is my favourite model, I say that makes it the best. It has a Plaguebearer head and a Nurgling. New Plague Marines never have Nurglings sculpted into them, but apparently the very latest batch released in 2017 do, proving everything old is new again. It has the classic go forth my minions pose. And is armed with a cool beast skull stock bolter.
When I repainted it, I gave it a special backpack. I believe it is a Legion of the Damned backpack, I bought it while at a Grand Tournament. I spent a lot of time on the face and non-armoured arm. I did a blend of brown and red. It came out pretty cool IMHO, but it doesn't photograph so great. This model has a lot of bone and I've gotten pretty good at painting bone over the years. The key is to not dry brush and to use multiple thin coats of paint. I also am lucky enough to have an old pot of Rust Brown Ink which I thin and use as a wash. I tend to use multiple washes and to use very little pure white on my bone. Sometimes I mix some Plasma Red ink into the Rust Brown. You can see the backpack in more detail over at CoolMiniOrNot.