Noise Marines are definitely the more shooty of the two. Plague Marines are quite good though; T5, Feel No Pain, Blight grenades... they're great for claiming and defending objectives. Plus, with Meltagun access, they're better at popping tanks than Noise Marines. If I were you, I'd take both.
As Fynn said, you can easily use green stuff (or just a nurglish paint scheme) to denote Plague Marines, and you can get regular CSMs on ebay for cheap. I'd advise stright-up buying the Noise Marines.
As Fynn said, you can easily use green stuff (or just a nurglish paint scheme) to denote Plague Marines, and you can get regular CSMs on ebay for cheap. I'd advise stright-up buying the Noise Marines.