Testament had a few clunkers in the early 90s, but other than that they have been very solid. The past 4 albums are all fucking amazing, though very different.
Megadeth got heavy again after a few years of total wimpy shit, yet they still suck (Just like Metallica). First 3 albums are all I care about, Rust In Peace is fucking overrated. The first two songs are great and the rest is boring as fuck.
Slayer is Slayer. Always a good time to see live, and Seasons is a strong album, but I'd rather hear South Of Heaven all the way through. Or at least have them bust out Spill The Blood, Ghosts Of War and Silent Scream some more...