I hate choosing a "best ever" for anything. I have more than one in mind. Brandon Boyd, Burt McCracken, Gerard Way, Chester Bennington & Mike Shinoda, etc.
Thom York of Radiohead would be up there for me, but that's very difficult to say. Best lyricist ever.....Radiohead's probably the only modern band I'd consider for it. I can't pick just one from the more classic era.
Gerard Way - My Chemical Romance Brandon Boyd - Incubus Davey Havok - A.F.I. Bert McCracken - The Used Trent Reznor - Nine Inch Nails
In rock only? hmmm. Joe Strummer of the Clash and the Mescaleros Brody Dalle of the Distillers Jesse Michaels of Operation Ivy and Common Rider Billie Joe Armstrong of Green Day Amanda Palmer of the Dresden Dolls (not exactly rock...but still) Courtney Love has some real gems too, especially on Celebrity Skin and Live Through This.
Trent Reznor Pete Doherty Tim Armstrong Jello Biafra Kurt Cobain Matt Caughtran Henry Rollins The Shinoda/Bennington partnership is pretty good on it's day.
these are prob the only good lyricists on this whole thread. corey taylor, chester and mike, etc. are horrible lyricists. davey havok is my #1 lyricist.
Brandon Boyd from incubus - his lyrics sound like poems when i read em' beatiful .. sniff sniff.. just beatiful
Amy Lee has some great lyrics, same with George/Wade/Dallas from Alexisonfire, Matthew Good, Scott from Finger Eleven, Yas and Bobby from Dead Celebrity Status. Chester and Mike were great before Meteora. Maynard is probably my favourite, he's amazing.
I think Amy Lee and whoever writes Nightwish's lyrics. AFI is on that list as well. I love Amy's because they're really well written and describe how I'm feeling like, all the time. I love Nightwish's because they're way out there and not many bands write about what they do. I love AFI because I love how they portray things and I love the poetic style of it.