I'd suggest a four ball roller that breaks down into two pieces EASILY---I've got an older Columbia bag that does that. (I just undo a couple of easy-to-reach clips and bang-- two pieces with a suitcase-type handle on the bottom part so it picks up real nice). If you're doing any amount of walking you'll sure appreciate the fact that you can roll it.  And breaking it down into two pieces will surely help in those situations when you've got to  tote them some.  I used to have two two-ball totes BEFORE the roller bags came out  and I can't imagine carrying those things any farther than out to the car, mush less to a bus stop, etc......  (Can't recommend the new Columbia bags, however.  They were having some production problems with them early on and I don't know if they fixed them or  not -- my buddy got a new Columbia bag and he was real disappointed with it).