1french we have an ergo and an osprey poco (frame backpack).
DH bought the Osprey (their standard backpacks are second to none) with DS1 but it's only been used a handful of times. I find it heavy and uncomfortable (unlike Osprey's other packs). The ergo, however, was used daily for the first two years and almost daily for another two (and then had a year off before DS2 arrived!)
DH says the ergo isn't comfortable for him, but it's the first thing he reaches for when he's supposed to be looking after the baby and he'd rather be doing something else. It's likely this is because he's been a bit rotund and would probably be better with an onbu style carrier or wrap (but he cba to learn how to wrap!).
Short answer: I recommend a soft structure carrier (ergo/boba/Beco/nova/Connecta/Tula etc) over a frame carrier. Second bonus is that they can be worn on the front, and third is that most of these will be useful up to 4 years.
TheM, I understand your conflict - I'll be back at work full time soon and that's partly why I'm happy (in theory) to feed overnight as needed. (But, he's still in the bedside crib so it's a barely waking slide-n-boob).
We didn't sleep well last night! No particular reason, to my knowledge. He woke up as I came to bed and was awake for about an hour till after midnight, fed at least twice and was WIDE AWAKE at 6am! Ah well, I need to start getting up early anyway!