I haven't tried any other pedals infront of a dirty amp, but I love my MXR ZW-44 Zakk Wylde overdrive. On a clean channel, you can get some smooth creamy bluesy tones up to hard rockin AC/DC tones, and infront of an already dirty channel, you can get pretty darn heavey if you want. It also adds more clarity and note defenition, so it works great for leads. I use it to beef up a PV Classic 50 and to tighten up a PV Triple XXX. I usually keep the level full up, the tone around noon and the gain to taste with the C50, and at 0 with the 3X. A tubescreamer or a Boss SD-1 would give you similar results.