Fresh start for a Noob

Are you planning on playing on multi accounts or just one? Because both rolls are really good in my opinion. 1st account has a standard good overall team for any situation since you have a (taunter D'Eon) (single DPS nuker Herc) (Aoe Trash clear Eliz).
As for your second account, well Florence is a situational but powerful support overall because she carrys a full kit of everything you want for a support (heal/dubuff/buff) (only downfall is she is a zerker meaning squishy).I never had the cat so no opinion. As for Frankentstein, to me she is a 1 time super AoE nuker, But relies on CE's that give her starting NP gauge else she will die before you are able to use it.
*Purely my opinion and experience with those servants.

Hmm...
Your first account is more balanced. However...second account has a 5* and a 5* is nothing to be pushed aside.
I still feel like your second account is better. Even with Herc's power level, your far more likely to see another Herc in the future than you are another Nightingale.

Since both are good I'd say you should pick one with servants you like more as characters

Another thing to consider, is that both Tamamo cat, and Frankenstein have Noble Phantasms that stun them. So you can't use then in a brave chain. Though... Nightingale's NP removes debuffs, so she should be a great support for the other two.
But that team will be very squishy.

I'd choose first account. Heracles is a 5* disguised as a 4* starter servant. Also d'Eon + Mash are a good defense for him and Eli is a good servant overall, only Stheno is mediocre.
Second account is nice cuz is nice to have a 5* just starting the game... but berserkers tend to die so easily. You'll have to rely a lot more on friend's support.
Anyway the desicion is yours.

1st account has good survivability but second account has a.support berserker 5*. Meaning you need a friend support that she will support