For the backpack carrier, as for front carriers, it's important to ensure that there's a wide seat platform for the child. Our kids are all grown up and I haven't looked at carriers in detail in a while but it used to be that the Baby Bjorn front carriers and Kelty backpack carriers were well-known to hold the child by the crotch, with legs dangling down and that's something to be avoided. For the front carry, Mei-Tais, most soft-structured carriers and many others provide that wide seat in the facing-in position. However, I've never seen a child carried at the front in the facing-out position who didn't have their legs dangling down (and to this day, I look at every child in that position that I come across, wondering if an OK facing-out option will ever become available). Of course, a good number of backpack carriers also offer a wide seat for the child. Back then, we used a Macpac Possum.
We also almost never used the stroller, opting for front-, then back-carrying until the kids could walk a bit, at which point we tried to have them walk on their own as much as possible, holding hands, praising, encouraging, taking little breaks and using the backpack carrier only when more serious rests and naps were necessary after good walking bouts. Once the kid hits that milestone of walking pretty reliably, the main thing is that, whether you're going to a crag, on a hike or just shopping, you should adjust your schedule, goals and speed expectations to allow for all those breaks and walking bouts at a toddler's pace.