The toddlerhawk is different than the other carriers mentioned. It is a mai tei (MT) style, which has straps that you tie on, where as the others are all buckle carriers (SSC-soft structured carrier) and you just click and adjust. The toddlerhawk is about 2" taller than the babyhawk, but structurally they're about the same. I find MTs and SSCs to both be pretty supportive, but your preference may depend on your build, the build of your child, whether front or back carries are more important, and how squirmy or sleepy your kid is. I made my own MTs and loved them when DD was little and I wore her in front. When she got heavier/taller, I preferred carrying her on my back and opted for the ease and extra support of my angelpack LX (again, very similar to beco). Another important difference between beco/ergo/aplx and the toddlerhawk is the waistbelt. With the toddlerhawk, you put it on by tying the waistband with the fabric rectangle hanging in front of you like an apron, then pull it up to form kind of a pocket, with the kid sitting in the crease. Then you pull the fabric behind kid's back and tie the straps either backpack style or you can criss cross. With the beco style carriers, the waistband has a foam padding that forms a shelf for the kid to sit on. These are usually designed to be worn lower on the hips to distribute the greater weight, like in a hiking backpack. Other than that, it's pretty much like putting on a backpack and the webbing can be adjusted and the chest belt clipped for a tighter, more secure feel.
I know it's a little longwinded, but just wanted to make sure you were aware how different the two types are. They are both good, and many people use either or both from newborn up. I've seen them used with 4 or 5 year olds even.
I think it will really depend on your frame and your kiddo though. Mine doesn't hurt my back at all unless I've been wearing it a long time, but it seems to kill my sister's back after only 30 minutes (he DS is bigger than mine though and she's smaller than me LOL). 
