acually you need to reconstruct your sentence and to give some information before (that will provide )
so depending in the context we can suggest in all or at all because it highly depend in that and both are right for some thing. Eg
we will provide maintaince service for all territories.
and for optimum and optimal they are partialy interchanchable
both can be used as adjective but more with optimal while as a noun only optimum work.
we will provide maintaince office at all territories