Personally, if I were looking at two guns 'til the end of time, I wouldn't want the 1911 as either choice. My advice is to sell the 1911 and get a Sig and a GLOCK or Sig and an H&K. I have both Sigs and GLOCKs (no 1911's...if you didn't already guess, I don't like them).
If you insist with keeping the 1911, I would recommend the GLOCK for other reasons than you listed. The GLOCK is much more rust resistant than a 1911 or Sig and therefore can last longer under different conditions than whichever other gun you choose. Also, I would recommend a 26 and not a 19. If you have a 1911 then get a smaller, more readily concealable gun. The 26 will still take all the high cap 9mm magazines, but will have the benefit of becoming small if needed.
If you insist with keeping the 1911, I would recommend the GLOCK for other reasons than you listed. The GLOCK is much more rust resistant than a 1911 or Sig and therefore can last longer under different conditions than whichever other gun you choose. Also, I would recommend a 26 and not a 19. If you have a 1911 then get a smaller, more readily concealable gun. The 26 will still take all the high cap 9mm magazines, but will have the benefit of becoming small if needed.