Rock Band 3

If you jump around from instrument to instrument playing this game, and play usually by yourself . Then voila! A list of every song in the game and what the game (or in the case of the same difficulty, the global leaderboard) says is the easiest instrument to play it on! You don't have to take these to heart, you are going to be better at one instrument than others and will probably play the songs on different instruments than the ones I stated.
"20th Century Boy" - Drums
"25 or 6 to 4" - Vocals
"Antibodies" - Vocals
"Beast and the Harlot" - Vocals
"The Beautiful People" - Keys
"Been Caught Stealing" - Bass
"Before I Forget" - Vocals
"Bohemian Rhapsody" - Drums
"Break on Through (To the Other Side)" - Vocals
"Caught in a Mosh" - Vocals
"Centrefold" - Drums
"China Grove" - Guitar
"Cold as Ice" - Guitar
"Combat Baby" - Keys
"The Con" - Keys
"Crazy Train" - Vocals
"Crosstown Traffic" - Drums
"Dead End Friends" - Vocals
"Don't Bury Me...I'm Still Not Dead" - Bass
"Don't Stand So Close To Me" - Drums
"Du Hast" - Bass
"Everybody Wants to Rule the World" - Guitar
"False Alarm" - Vocals
"Fly Like an Eagle" - Guitar
"Foolin'" - Drums
"Free Bird" - Vocals
"Get Free" - Guitar
"Get Up, Stand Up" - Guitar
"Good Vibrations" (Live) - Guitar
"The Hardest Button To Button" - Guitar
"Heart of Glass" - Keys
"Here I Go Again" - Bass
"Hey Man Nice Shot" - Drums
"Humanoid" - Bass
"I Can See for Miles" - Bass
"I Got You (I Feel Good)" - Drums
"I Love Rock N' Roll" - Bass
"I Need to Know" - Drums
"I Wanna Be Sedated" - Vocals
"Imagine" - Bass
"In a Big Country" - Drums
"In the Meantime" - Keys
"Jerry Was A Race Car Driver" - Vocals
"Just Like Heaven" - Bass
"Killing Loneliness" - Drums
"The Killing Moon" - Keys
"King George" - Vocals
"Lasso" - Drums
"Last Dance" - Guitar
"Living In America" - Guitar
"Llama" - Vocals
"The Look" - Vocals
"Low Rider" - Guitar
"Me Enamora" - Guitar
"Midlife Crisis" - Guitar
"Misery Business" - Guitar
"Need You Tonight" - Keys
"No One Knows" - Vocals
"Oh My God" - Keys
"One Armed Scissor" - Bass
"Outer Space" - Drums
"Oye Mi Amor" - Bass
"Plush" - Drums
"Portions for Foxes" - Vocals
"The Power of Love" - Drums
"Radar Love" - Keys
"Rainbow in the Dark" - Keys
"Rehab" - Guitar
"Rock Lobster" - Keys
"Roundabout" - Vocals
"Saturday Night's Alright for Fighting" - Vocals
"Sister Christian" - Bass
"Smoke on the Water" - Guitar
"Something Bigger, Something Brighter" - Vocals
"Space Oddity" - Vocals
"Stop Me if You Think You've Heard This One Before" - Drums
"This Bastard's Life" - Drums
"Viva la Resistance" - Bass
"Walk of Life" - Drums
"Walking on the Sun" - Drums
"Werewolves of London" - Vocals
"Whip It" - Vocals
"Yoshimi Battle the Pink Robots Pt.1" - Bass

This achievement requires you to 5-star every song on the RB3 disc on hard. You do not need to use the same instrument for every song, as long as you get 5 stars.

If you have a bit of experience with RB or GH you shouldn't find this too tough, I'm not especially good and the only song that really gave me grief was Caught In A Mosh which I eventually beat on bass. A lot of the top tier songs are noticeably easier on guitar than bass, or vice versa - 25 or 6 to 4 is a lot easier on guitar.

Easiest way to fire this up is through the My Goals menu.

Thanks to iHeartForeigner who has also suggested: "check in my goals, and you want to look under "rock band", then "band song progress" then the goal that is the hard difficulty and select it and you will play what you have left. credit to GoodSmeagol for this"