P45 has a valid point, most could not handle the requirements for a mature Vittatus. 6" is a very large Goliath. The world record Goliath is 6'6" and it weighed a staggering 253lbs. Most of the large ones caught on rod and reel there are more like between 4-5' and weigh about 75-125lbs. There are a few among us capable of effectively raising and maintaining a full grown (4' or so) Goliath.
As far as preference, they both have pros and cons.
Vittatus
pros: More attractively patterned and have more color. They don't get as large.
cons: Far more aggressive among ATFs, and seem a bit more nervous.
Goliath
pros: Less aggresive among ATFs, not as skittish, and have bigger teeth at smaller size. A much rarer fish in the hobby.
cons: Get huge, are not as colorful or as attractively patterned.
I prefer the Goliath myself, but I also keep Vittatus cuase they're bad ass too!