Of the packs currently on the market and readily available, I like Ruffwear. One caveat is the fitting. Best to try them on when the dog is fully mature. I have had some mods done on both of my packs; fortunately, there is a tack shop in town that also has a repair shop. Personally, I like the style where you can leave the harness on and lift the pack off.
Make sure that both sides of the pack are loaded equally and have a scale available as the
weight needs to be equal. Until a dog is fully mature at 18 months, keep the weight at a minimum. I do get mine in packs before 18 months but stuff something light like a jacket in them rather than any real weight. You also want to keep all the straps next to the dog clean, as any debris in them will cause rub marks. I have all my straps wrapped, in easy off and on for cleaning, real sheepskin halter pads. Check online or at a local tack shop for these. You want the real sheepskin not the fake stuff.
Here are the two packs I have.
This one was purchased in the 90’s for my current girl’s uncle. It was a large and straps were modified to fit Tara. (red pack in pic)
Wenaha Dog Packs
Rex has this one from Ruffwear in large and I did have the straps taken down some. It actually did fit with the available adjustments but I wanted them centered a little better.
Palisades Pack? - Ultimate Backcountry Dog Pack
FYI, REI has all Ruffwear at 25% off with the sale ending TODAY.