People hate my answer, but the best survival pack is the one that carries all your items you need to survive while making it relatively comfortable to carry for an extended period. Most people shop for a pack, then all the items, and find out that the pack is not sized appropriately (usually too small) for what you need to carry.
Depending on the use of the survival pack, get all the items, and try to consolidate in an orderly pile to figure out how much space you will need. Then, shop for your ultimate pack. I will review a few packs I use for various use cases and may help you decide how to find the right size and right comfort pack.
Finally, ask yourself these questions. Do I really all that stuff for this specific use case? Can I find a lighter item that will do what I need for a specific function? Can I carry this weight for a long time for what I am doing (i.e. day hike, camping, survival bag)?
Make sure to get the best gear you can afford that is compact and light that will work for your needs, wear what you can on your belt, and if possible, find multifunctional items. Also, think of how you can attach some items to your pack or on your belt instead of stuffing it, like a flashlight on a clip, GPS mount for your shoulder strap, knife mounted on your shoulder strap, headlamp in a belt mounted pouch, etc. This way you can keep the weight off your back and distributed around your body.