Just a few notes:

 Yea, you see it (probably not in-GAME tho ha haaaa...), it's hands down BiS. It's VERY hard to come by considering it doesn't drop from Midtown Gobbo for whatever godforsaken reason; only Bugle and maayybe Doom terminal (there's conflicting info about the latter). I dropped SAW BEFORE I found this as a cosmic and I'm not alone in that regard. I know the title is "DEFINITIVE" in all-caps but ultimately "BiS" =/= "required". At least in some cases....  IS actually required for this build's power rotation to function properly unfortunately :/

 is better than Attilan I know... just like it is on every other character. As a functionally full area-tagged build, movement Spidey can run  without feeling bad about it, while freeing up your Atlantis stacks for the other ~62 heroes on your account ;) 

  is better than Spidey's own  but it's close. If you've had rotten luck when it comes to CHT drops, or   giving you garbage like me :)))) you can use his personal slot 4 and again not feel too bad about it. Especially considering Spidey isn't a power duration merchant like a lot of the other heroes Skrull uniform is BiS for are.

On the insignia: The generic recommendation, especially for characters with no auto crits/bruts, is crit damage/rate... but Spidey is a ~100% area tagged hero getting a big chunk of effectively unconditional crit rate from   together with the rest of his gearing and IP investment. Uniquely positioning him to take good advantage of area damage on insignia, which unlike brutal damage for example (which rolls prohibitively poorly for its stat weight here) rolls pretty generously up to 500; higher than melee, ranged, AND boss damage in the same slot by 100 points or more. Crit rate vs brutal rating vs flat damage on item slots like this, and the balance between offensive stats in general is a subjective caclculus that will vary depending on YOUR personal rolls on gear, total number of infinity points and how they're allocated, available synergies, potential diminishing returns on certain stats, etc. What you choose for this slot will almost certainly just come down to whatever's rolled best in your own stash/inventory at the end of the day.  

On vulnerability: Spidey is in the awkward position of possessing a crap vulnerability power   that should actively be avoided outside of levelling, not scaling on either mainstat found on , and being outright unable to equip Anti-Metal ammunition (which hilariously would be a fine placeholder for  on him if he WAS a "gun hero"). Meaning you will have to lease his vulnerability application out to either your teamup hero, one of your artifact slots, or other players in group content. Your best and most reliable choice will be to just put the   in the bag with a 10% sig CD cosmic affix on top. Relying on a teamup as your sole avenue of vulnerability upkeep is generally NOT recommended in practical gameplay for a variety of obvious reasons. But if you do choose to go this route... your best option is:   followed by either of . The vulnerability power from  is decidedly worse than the aforementioned three, having a noticably lower duration than its cooldown (among other issues) and as such is terminal levels of cope/not viable. If you're only ever going to play in patrol zones or raids with other people, you can be "that guy" and just not run a vulnerability source of your own at all as you mooch it off of others. But of course that's a non-starter if you're ever on your own... so try not to be "that guy" if you can help it ;)