Which tank is better?

i plan on getting a large tank, somewhere between 75 galon and 125 gallon. i havent made up my mind yet.(probably the bigger one). i want to do planted cause im really into aquascapeing. im wondering, is it better to longer or taller? ive thought about adding discus..so i know i would need taller if i went that rout, however im not sure yet. i want to have a huge shoal of Cardinal tetras, probably 30 or 40. and i want 5 otos, 5 drawf corrys , and MAYBE 10 diamond tetras or something simular. i want two types of shoaling fish cause i want to see the cardinals shoal tightly. i want a verity of fish sizes...so my real qustion is.....which is better, the longer and shorter tank, or the taller and less wide... ill be doing alot of planting and alot of aquascapeing. ill be haveing pressurised co2, canister filters, either t5ho or power compact lights...aquasoil, etc the whole nine yards.