My preference is the ERGO. I started out with a MT but just couldn't stand getting the straps dirty when putting dd on. It was also a pain when I had to take the time to make sure the straps were not twisted. For the long haul, I just couldn't get her comfortable. Wherelse the ERGO is my workhorse carrier. My slings are what I use for quick trips but I won't go anywhere without the ERGO now. It's quick and easy and SO comfortable. It's also the only carrier I can nurse dd in comfortably. The other big seller is that my husband loves the ERGO! He's a chiropractor and fully endorses it. So it's versatile for both of you.
It does come down to personal preference. I loaned my MT to a friend who loved it and to another who prefered the ERGO.
Good luck! Either carrier will be great