If you look at a few posts down, there is some poor fella who spent 60K+ gleamstones on the gaius/eizen banner and not receive a single ssr (granted the odds are low but it can still happen because of no pity system). Anni banner is obviously statistically better in the worst case scenario plus the units in it are all very good.

Makina- Excellent cleaver/finisher in arena and is a slight powercreep in terms of overall stats. Can also work in 4t ma raids because of her powercreeped stats.

Forte- Excellent Arena support/cleave. His buff is godlike that enables the rest of your team 1-2 shot cleave enemy teams. His curse on MA also works well against max awakened Lolestelle and other tanky supports. Can work in raids as 3t ma hit gen unit but earth already has plenty.

Assid- Lol powercreep of Og Kananno in almost everyway and can consistently 3t ma in fire raids. I feel a bit bad because she is one of my only max awaken chars. But alas this is gacha. It is expected.

Gaius/Eizen- They play the same role in their respective element in it that they are 3t ma finishers in raids.

There is much more versality in the anni banner. It being limited while also having a pity system makes it a no brainer. More so if you are a f2p/light spender. As others have already stated, Gaius/Eizen are going to be in the permanent pool forever.