depend on what way you will use them, 1000 G tank cost more than 10 100G tanks. Some kind of fish can't be keep together, so you can't throw them in a 1000G tank!
I would like to have the 1000G tank only if I already have some 100G and 200G tanks to back up in case of sick or injured fishes need to be seperate; also depend on how it will fit in my house!