um... no such thing... as THE BEST bag...
but before we get to that... are you going to carry all your gear when you are up skiing?
or are you looking to carry the essentials in a backpack, and have a way of traveling with your gear to your destination?
personally, i don't think i've ever recalled anyone skiing with their laptops and the ENTIRE range of lenses...
so, if you are looking for a backpack to carry essential gear, you may, again, consider some of the greater recommendations such as F-Stop and Thinktank.
if you are looking for a backpack to ferry gear to your destination, then yea, large ICU or better yet, something with a harder walled bag such as Lowepro traveler case and such.
i've gone through a couple of bags, not as much as some here but here's my take.
TT-Streekwalker:
great construction, 1 body with long lens and some accs, or 1 body with couple shorter lens and accs... no problem. only wish they had a better way of securing tripod on the side instead of the middle of the bag.
Kata 3n1 30:
crap construction, piss poor construction... interesting design but the stitchwork and materials really sucked. not the most comfortable bag
Lowepro Pro Trekker AW:
on par with TT in terms of manufacturing quality, stitchwork, and fabric materials... very good... very very good... but i got this bag thinking i will carry all my gear... somewhat equivalent of your list... and realized... no... i will NOT lug all this gear with me... unless i'm going to be out for a while and i MUST carry all this gear on me.
F-Stop Tilopa
comfortable...
fabrication, materials, stitch are all good... but one minor detail... i've purchased this used but realized that the metal tubing frame actually does a number on wearing out the fabric and coating when exposed.
bag fabric is usually coated with 600 to 1000mm (wp rating) polyurethane coating... and they eventually rub off if exposed to hard surfaces.
but aside from that, i love the versatility of this bag... the various ICU sizes, (i have 3 sizes) accomodates to your needs and also can ferry the wider range of gear from one destination to another... then replace ICU to smaller to carry your essentials.
but i would still take a secure bag to lock my gear in hotel.
my vote is, spend the money and get a single system that will accommodate your needs... hence, F-Stop Tilopa or Loka and the inserts in various sizes...
it is very comfortable.
i think i may sell my TT and get a Loka.
cheers.