Chain or tree?

Dear all,

    I was wondering whether there is a difference in performance (memory, mainly), in case one chains some trees written on files using a TChain, or building a TTree with CopyEntries. I have tried to see what happens using gSystem->GetMemInfo(), and also with "top", but it seems as if there's no difference.... Am I wrong? BTW, which is the "best" solution?

     Thanks in advance. Cheers,
                         Chiara