I've heard of those two bands, but can't say that I've heard their stuff, or if I have, I can't recall what they sounded like.
I love the sound of two dueling and/or harmonizing guitars, a bass that is more than just rythem, machine gun fire double bass drums with a skin beater who knows how to use every piece of his 38 piece kit and a lead singer with a fluid, melodic voice that can hit teh highest highs and the lowest lows.
Granted that doesn't really describe Dave Mustaine's singing but Megadeth just plain kicks your ass and makes you say, "Thank you sir! May I please have another?"
If I had to choose between Maiden or Helloween as my favorite band, I think my head would explode.
Thanks to XM radio, I learned of several new bands (or at least new to me) that don't get played on regular radio because Hard Rock stations don't acknowledge a band unless they're Metallica.
My favorite newer band is a six piece act out of England called DragonForce. When I first heard them, the song was "Operation Ground and Pound." It started in with the awesome guitars and uberfast drums, and I waited for a minute and half, wondering, "Will this be a great, smooth sounding voice, or just another death-metal Cookie Monster singer?" So happy to hear it was the former. I don't have any problem with the Death Metal sound, the music is awesome, but the growl singing wears quickly on me.

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The United States will conquer Terrorism with the help of God and a few Marines.

Some people, when trying to avoid thinking about those things that cause them pain, turn to drink, or perhaps food, or drugs... I turn not to any of those... I collect action figures, turning my mind to the hunt, so that I might find a mote of peace... Over the years, I've found that alcoholism is much more socially acceptable by far.