I vote "panniers" all the way.
Messenger bags and back packs are okay, but "sweaty-back" in the 3 seasons out of the year sucks.
Saying no, to back-pain - I went with panniers and never regretted it.
Some small rides I still break out my Chrome bag for.
(there's my two-cents worth
)
"Things look different from the seat of a bike carrying a sleeping bag with a cold beer tucked inside." ~Jim Malusa
2009 Trek 520-Brooks B-17 Special in Antique Brown
2010 Surly Long Haul Trucker-Brooks B-17 Standard in Black
1983 Fuji Espree Single Speed-Brooks B17 British Racing Green