1. Metallica - They've had peaks and valleys for me, but they're overall the consistently great hard rock/metal band that I can almost always put on and enjoy. They're the consistent throughout my life, from my early teen years until now. Hetfield's gritty singing style is powerful and unique, and his riffs are infectious. Master of Puppets is probably still my favorite album of all time. Kill 'em All just gets me going with its raw riffing, and even more of their straight up heavy metal and hard rock stuff can be enjoyable.
2. Sonata Arcitca - Marked the beginning into my foray into some of the lesser known metal out there, particularly the European stuff. Helped me through some dark times during my college and some post-college days shortly thereafter. Love their emphasis on melodies while still having some moderately heavy stuff, and their somewhat experimental nature which their sound has noticeably evolved and morphed little by little with each album. Very underrated band, at least here in the US.
3. System of a Down - Pretty much my gateway band into heavier music, and one of the first bands I got into. But unlike the other gateway metal band I liked back in the day (Linkin Park), these guys have stuck with me over the years. Love Serj's unique singing voice, John Dolmayan's drumming, and their lyrical themes and messages (though it gets a touch watered down by Hypnotize/Mesmerize). They manage to be unique, yet familiar with their sound, and walk the line of heaviness and catchy, accessible tunes.
4. Megadeth - First, Dave Mustaine is my favorite guitarist and one of my heroes. His autobiography was simply fascinating and inspirational to me, following the crazy roller coaster ride of his life, and how much shit he had to endure and fight through to get where he is now. While Metallica I tend to prefer the riffs, Megadeth is my go-to for the face-melting guitar licks and shredding solos, most of which beat Kirk's stuff hands down, or most other bands I've heard for that matter. Like the diverse palette of sounds they've taken on over the years, and the political (semi-conspiracy theory type) themes.
5. Black Sabbath - More of a recent discovery with me, but these guys have quickly rocketed up my list of favorite bands. Tony Iomi's story of losing his finger tips and essentially inventing the heavy guitar sound as a result is intriguing and inspirational. His riffs are just unmatched in their catchiness and musical/emotional impact, and of course, Ozzy's unique wailing voice has an appealing, distinct charm to it. Love Geezer's base playing and his lyrics as well. I even like some of the Dio era stuff, as it's got a bit of a power-metal vibe. I keep discovering more and more music by Sabbath and one song after another I find I just love more often than not. My next goal is to delve into some Tony Martin-era stuff.