i've got a soft sided box and would never switch back...
main reason is you can buy a whole whack of plano boxes and load the ones you will need, and leave the ones you don't...
ex. you don't need bass tackle when going salmon trolling...
the shoulder strap is nice depending on how much stuff you load in... the more you load in it, the more soar your shoulder gets...
this is the one i have and it can fit 6 3700 size planos in there, and i have another 15-20 at home...