My favorite song is: Eminem – Survival. I think, it's self-explanatory why.

If you are curious, here is my all time best for gym playlist:

• 50 Cent - Get Up
• DMX - Where The Hood At
• DMX - X Gon' Give It To Ya
• DMX - Party Up (Up In Here)
• Dr. Dre - Still D.R.E. ft. Snoop Dogg
• Eminem - Till I Collapse
• Eminem ft.Nate Dogg - Shake That
• Eminem – Survival
• Eminem - One Shot Two Shot
• Eminem - You Don't Know ft. 50 Cent, Cashis, Lloyd Banks
• Eminem – Welcome to Detroit
• Hollywood Undead - Everywhere I Go
• Muse - Supermassive Black Hole
• P.O.D. - Boom
• Rammstein - Links 2 3 4
• Rob Zombie – What

I can listen to it non-stop. Usually I add/remove 10-20 more fresh songs to it once a month. But these babies stay put.