As someone who's painted over 100 plaguemarines, 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 Plaguemarines never have Nurglings sculpted into them... 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.