I've preached about Guitar Freaks here numerous times in the past (in recent memory, once to Sami and another time to American Nightmare), as it's one of my most favorite Bemani series of all time. Some folks may try to compare them to Konami's own 'Battle' series, which I believe is a bit unfair, because GF doesn't restrict itself exclusively to the hard-rock genre. Instead, it focuses on a diversified mix, done up in many different guitar styles, ranging from jazz, blues, metal, surf, pop, country-rock, and yes, hard-rock. The later mixes went on to include some questionable covers of licensed vocal songs from the East and West.
My highest recommendation would most certainly be 2nd Mix; not only does it include *all* of the main tracks from the first album (minus the Long Versions), but it also includes about twenty three new songs exclusive to 2nd Mix. I'll save my rant on how the series gradually plummeted in quality from 4th Mix on, but for an introduction to the finest of Guitar Freaks, you can't go wrong with 2nd Mix.