6 on the left is more symmetrical. There's 7 keys on the left side of the top row: ~0123456. There's also 7 keys on the right: 7890-= and backspace. Also, th

6 on the left is more symmetrical. There's 7 keys on the left side of the top row: ~0123456. There's also 7 keys on the right: 7890-= and backspace. Also, the standard staggered layout is not quite symmetrical. 6 is slightly to the left of the midline between the two index finger home keys of F and J, closer to the left hand. If you're an accountant touch-typing lots of numbers, breaking it to 12345 and 67890 would make sense. But for anything that involves more of the keyboard, certainly including programming with frequent use of the - and = keys in the top row, breaking 123456 and 7890-= makes more sense.