Guild Wars 2

Okay, so if I want to increase my storage, I can spend 600 gems to get 30 vault slots (20 gems per slot) or 400 gems to get an extra bag on a character (20 gems per slot best), or I can spend 800 to get a new character slot with a potential 100 slots with no unlocks (8 gems per slot). So, ignoring shuffle-time, the most efficient way to upgrade storage is unlocking more character slots, right?

Or making your own personal guild, with you as the only member, and gaining enough influence for a guild bank

It depends on a few things.

For a start in order for a new character to have 100 storage slots you’d have to buy 4 20 slot bags, which at the moment would cost you about 40g minimum. So you’ve got to factor that cost in too.

Secondly a storage character can only hold things that aren’t soulbound. (A personal storage guild can likewise only hold things that aren’t soulbound or account bound.)

So I’d say it depends on what you want to store. If you need extra space for crafting materials or other unbound items then a personal storage guild is the cheapest and easiest. If it’s account bound then another character is best.

If it’s soulbound, for example weapons or armor for one of your characters then you’re better off buying a bank tab or bag slot (depending on how many slots you need and how many characters it’s for).

(Oh, one other thing to bear in mind: Remember that extra bags are specific to the character, not the character slot. If you delete them then you lose the upgrade.)

https://forum-en.gw2archive.eu/forum/game/players/Bag-slots/3876352
and
https://forum-en.gw2archive.eu/forum/game/players/Bag-slots/first#post3880162

the cheapest options:
guild bank 50 = 10s/space
guild bank 150 = 30s/sapce
guild bank 250 = 42s/space
bank expansion = 1g80s/space
new character with 4×18-slot bags = 87s/space
new character + 3 bag expansions with 7×18-slot bags = 1g33s/space

(yes, 18-slot bags are cheaper than all other options, when you include the cost of buying the character, otherwise 15-slot bags are cheapest per space)

Keep in mind the security risks of a Guild Bank if your account is ever compromised (ANet will NOT restore Guild Storage). You also cannot access Guild Resources (purchased upgrades or any items stored in the Guild Bank) after a Home World Server transfer. All the upgrades and items will still be there, you just can’t get to them.

also, I find guild banks the least convenient. mostly just that you have to drag everything one-by-one. with the bank, you can double-click everything and it’ll move in there in like 10 seconds. It is literally faster to move 50 items to the bank, go get your alt character, move them to your alt, than it is to move 50 items into a guild bank.
but guild bank is the cheapest… I think that is intentional (cheapest being least convenient and most expensive being most convenient)

Yeah, I’ve found the guild bank to be the most worthless and most risky of storage options. When I upgrade next it will definitely be my bank slots. They are great for everything, especially account bound items.