Bank Alt VS Guild Bank

Most of the guild has at least one bank alt and now with guild vault in patch 2.3, is there still a need of a guild-bank alt.

Cost
Guild Vault:
100 gold for first 98 slots, 250 gold for second 98 slots, i.e 1.8g per slot.
Guild vault provides as many as 588 slots for 9350g, i.e. 16g per slot.

Bank Alt:
Bag slot in bank: 10s, 1g, 10g, 25g, 25g, 25g, 25g = 111 gold
Using 11 Netherweave Bag (16 slot) for 4 bag slots and 7 bank bag slots, 5x16 (bags and backpack) + 28 (bank) + 7x16 (bank bag) = 220 slot
Nethweave Bag costs around 8 gold each at auction house = 88 gold
Thus, 199 gold for 220 slots in bank alt, i.e. 1g per slot.

Guild bank alt costs a lot less per slot but the max slot limit is lower and it will occupy a character.

Accessibility
Guild Vault:
Guild master can permit as many as all members to access the guild bank.
Bank Alt:
Only the owner of that alt can access.

Guild vault is opened 24-7 in principle.

Level of control
Guild Vault:
Once permission are given, there is limited option of control over the deposition or withdrawal.
Bank Alt:
The owner of that alt has full control.

Bank alt can decide when, how and which items can be deposited and withdrawn.

Transparency
Guild Vault:
It depends on the permission given by the guild master. Usually everyone can look at it, therefore high transparency. Also, every deposit or withdrawal is logged.
Bank Alt:
Needless to say, low transparency.

While control was a issue for guild vault, the log pages are extremely useful for both control and transparency purposes.

Conclusions
Guild vault slots cost a lot and they cost more and more the more slots one purchase. However, its advantages are superior to the cost. The high accessibility and transparency (esp. the log pages) ease the management a lot. Good stuff costs.

If your bank alts has been selling things (such as flasks, potions, enchanting mats), guild vault should be able to replace this function if the trust level in the guild is high. For example, if I deposit a void crystal, and then withdraw 15g according to the guild price list. Then I withdraw five mana potions, and then deposit 10g (2g each).

For guild bank alt, the trust lies within the character owner. For guild vault, the trust lies amongst all guild members with access. If everyone is discipline, use common sense and follow the rules, the guild vault will ease the burden on officers a lot.

More general info on personal bank and guild bank.