What is the better call center solution? To have a big centralized center or have more but smaller local ones?

Both the systems have their merits and de-merits.
In the centralized call centre the issue of accent, local speaker etc are there but at the same time the operational overheads are within control. 
However for smaller local call centre, the overhead cost will increase. 
But if we are thinking the call centre only for one country then one centralized call centre is preferred then the local ones with Toll-Free number. 

i believe the more we get small centered call centers the more better results we get,less expenses,better work environment,more geoghraphically ditribution,less maintainance coasts .