Easy: Tom Petty songs, both Ron and Howie. Not difficult, but groove hard.
I've had to learn a handful of Tom Petty tunes just in the past couple months for some local gigs, and I gotta admit, they are fun as all getout! Really easy to learn the changes -- tbh I suspect Petty only knew the bog standard cowboy chords -- but the magic happens in how tight/compelling the groove is, and how the multiple guitar parts get orchestrated around those simple chord changes.
Hard: Hello Jeff - Stanley Clarke. Very fast sig line dbl w/ Beck.
Fun but difficult double stop groove section under Beck's solo.
I'm pretty sure Jeff Beck is not doubling the fast signature line in "Hello Jeff". Rather, that's Stanley overdubbed, either on a Yamaha organ, or a piccolo bass through the Maestro Universal Synthesizer System.
btw, if anyone has a transcription of that lick, I would love to see it!
And yeah, the stuff Stanley is doing underneath Jeff's solo is off the hook! Total thrash power chord mayhem!