It depends entirely on the amount of resources you need to store at one time. However, I would recommend the Modular Taskforce Cruiser because of the amount of storage it has and its versatility. It has a hangar and docking bay so it can store vehicles and ships as well as a high passenger limit. The MTC is basically a mobile base or if you are a merchant-type individual it could be used as a mobile shop.
What you should do is first figure out the exact type and amount of resources you wish to store, figure out their total weight/volume and then decide which ship type is more convenient/efficient. You should also remember to decide based upon the amount of time required to pickup and move all the ships you buy as well.
Rough cost estimate though the ship costs will most likely have changed since I last checked.
MTC: 150,000,000 credits
BFF-1: 21,000,000 credits
Brayl: 7,000,000 credits