I have the Sutemi and the Ergo. Here's my comparison that I've posted (it seems!) everywhere! For those of you that have already read this at TBW, BW, etc... apologies.
I find the Sutemi more comfortable and easier to use for front carries. The waistband is more flexible so it seems to fit better, and the straps are easier to deal with. Doing the chest strap up behind your back with the Ergo is a bit of a pain, and while I can use it for a back carry without the chest strap it doesn't feel quite so secure without it if I'm doing a front carry. (Shoulder straps keep slipping.) That said I would never reach for either of these for a front carry. I find the Moby Wrap, EllaRoo or Girasol much, much more comfortable for longer term, and a ring sling or pouch much better for quick trips.
The Ergo is easier to get on your back. Just lift the straps over your arms and tighten. The Sutemi isn't especially hard, just not quite as quick/easy as the Ergo.
It's much easier to adjust the waist strap on the Ergo. I find it a real pain to go from one size person to another with the Sutemi, but no big deal at all with the Ergo.
The sleep hood on the Sutemi seems useless to me. There is absolutely no way I could get it up over Fallon's head while she as sleeping. One, it's impossible to reach yourself. Two, her head wouldn't even fit under there! I imagine I'd have better luck with the Ergo sleep hood, but I've never had occasion to try it yet.
For some reason I feel safer with the Ergo. The shoulder straps ave no release clip, so maybe it feels like less potential points of failure to me? I'm not sure what it is exactly, but when I wear the Sutemi I find myself reaching and checking the clips and webbing constantly. I don't even think about it with the Ergo. (And I think about it even less with something that fastens using knots. Guess I trust fabric more than plastic.)
I like the overall look of the Ergo better. The Sutemi straps are *so* large and unflattering across my chest. The Sutemi is fine around the house or if I'm wearing lots of layers, but I find it embarrassing to wear with just a t-shirt. By contrast, I think the Ergo looks really cool and sporty.
My husband likes the Sutemi better. It's the first carrier that he's ever actually picked up and brought to me asking how to use it. I think the look appeals to him more, and I know he finds it more comfortable.