Gabriel would be my preference as he looks more developed. He'll be playing for Brazil before long so i think its a starting player + will grow in value.
Todibo i think is maybe 1-2 years away, could be a good rotation option now with Mina.
I think if we go for both then Keane would be off and Mina following him out the door next summer if Gibson progresses.
Todibo i reckon has the higher ceiling because he has everything including the same turns as stones used to make for us. However hes still a risk as hes not as far along as gabriel.
Value is with Gabriel even at £30mil as i think hed be a key player next to Holgate.
They signed him for free i think and can bank €20mil+ for him which helps their need for €70mil to cover FFP or something...most of tgeir squad seems to be for sale.
If you can find his games online before the virus you'll be surprised. He looked really good for barca.