You should use the filing center for the address at the time of filing. Ultimately it really makes no difference where the tax return goes, as long as it is an address that is still open or still has a valid change of address.  

If you are e-filing, it makes absolutely no difference.

If you are going to mail, I like to put each return in a separate envelope with the year and form number on the envelope. Then put all those envelopes inside a large envelope (e.g. USPS Priority mail envelope) with a short cover letter - PLEASE PROCESS THESE RETURNS AT THE SAME TIME.