is it better if I put a players tools(for data storage) in ReplicatedStorage so I can access it with a local script, or is it better to store it in a serverstorage(I have to create a serverscript to go through everyones guis)
Use server script. ReplicatedStorage would allow any player to take any tool inside there with a line of code. Easy hack.
It depends on what you need it for.
Replicated Storage is accessible to the client and to the server. Server Storage is only to the server.
If it's something really important store it in server storage.
Tho if it's for tools I would recommend server storage if possible.