Iron Maiden is such an amazing band. They were probably one of the first metal bands I ever heard, and when I got into them when I was 12 years old (like many other bands I discovered), I got deep into Maiden. I first purchased greatest hits, and the material I liked the most was their early work, so later I got Killers. I loved that album, but wanted to hear more Bruce Dickinson era Maiden so I got Matter of Life and Death. I just love Iron Maiden, they are a metal band, but they are also melodic and have high pitched vocals compared to other metal bands like say, Metallica or Pantera. Maiden will always be one of my favorite bands.
Megadeth were the second metal band I discovered. I was really into early Metallica at the time, and I knew about the drama with Dave Mustaine leaving the Band. I decided to try out his own band, and I instantly fell in love with the song "Holy Wars", because it had the thrashy intensity of Metallica with the melodic sense of Iron Maiden (whom I also discovered around the same time). I love Dave Mustaine's smart alleckey lyrics and attitude, and I think Megadeth are a bona-fide awesome metal band.
The first metal band I got into, I love Metallica, but at the same time I don't think they're the huge gruff insane heavy metal band that they are said to be. I would call Metallica more of an alternative metal band, because they've experimented with different sounds on albums like Load and St. Anger. However, they are still a great band, they just got a bit off track in the 90s. My favorite era of Metallica is the Ride the Lightning/Master of Puppets era because they had such a badass progressive sound, but still kept it angry and aggressive. Metallica are awesome to this day.
#2: Lamb of God
Lamb of God combine every extreme sub-genre of metal and mix it on with hardcore punk, creating the ultimate elite extreme band I can think of. Their riffs are awesome and complex, their drumming is thrashy, and Randy Blythe's cookie monster vocals are perfect. I also like to band's lyrics and concept. My first concert was Lamb of God and Anthrax, and that leaves Lamb of God a special place in my music world.
Anthrax is awesome, energetic, kick-ass. I love how they are a metal band, but they sound punky as well. Among the Living is my favorite album to play guitar along to, and Anthrax was my first concert, along with lamb of god. I have loved Anthrax ever since I first heard "Got the Time" and "Indians". Horns up to Anthrax!