An ackie takes up very little space, a 4x2x2ft area is plenty for 1, they cannot do severe damage if they bite, or scratch but can still really hurt you.
Argus are a medium to large sized monitor that can reach 5ft and are very nervous, active, bottomless pits, and can put a good hurting on you.
BTs are a large species take up huge caging, and get very big, they as well argus eat alot!!!They can do some very bad damage to you if your bit and can rip you up badly scratching.
Do you have 4x2x2ft of ccage, 4x4x8ft of space for a cage, or 10x5x4ft of space for a cage for 1 animal? Thats the first consideration, also can you afford the food for either larger species? Vet bills can be very expensive, and most BTs are wild caught, many argus are CB, but all ackies are CBB.