It depends on what kind of personality you are and what you make of your situation:
IMHO:
Walgreens
Pros: Best technology,most efficient pharmacies, OT, Night shifts
Cons: Drive-thru, volume driven, worst customer draw
Basha's/Food City/AJ's
Pros: Easy customers, Cohesive pharmacies, responsive managment, no drive-thru
Cons: Primitive QS1 System/Technology
Wal-Mart/Sam's Club
Pros: Best technology, staffing is adequate
Cons: Would you like to be a health and beauty manager too? No interns.
Fry's (Kroger)
Pros: Moderately paced, staffing, OT, responsive managment, No Drive-thru
Cons: Differential Pay Scales
Safeway
Pros: Friendly environment, moderately paced
Cons: (In AZ) Unresponsive to overly belligerent managment, "Smile School"
Albertson's/Osco
Pros: Cohesive units, OT, Nights
Cons: Inadequate technology to volume ratio (that's changing), New drive-thru models, Changing paradigms in pharmacy operations
Target (and K-Mart)
Pros: Cohesive Units, Relatively responsive management, easy customers, Low Volume
Cons: Who's heard of Target pharmacy?
CVS and Eckerd are still relative unknowns here, so we don't know their habits.
And things that are pros for me are cons for someone else. For a young pharmacist, punishing them involves taking away overtime. For an established pharmacist, punishing them involves forcing overtime. You really have to what you want and match it to the right company.
I know of several cases where pharmacists bounced from company to company to find the right fit. If you have the opportunity, try to pick a diverse set of companies for your clerkships and treat it as a 5 to 6 week interview. You can save yourself a headache when contract time comes.