If its a train expected to have heavy demand for the date of travel, its better to do 6+6+1 to ensure that you get as many seats confirmed as possible.
If booking at the counter, you might face challenges from people behind you objecting to 3 reservations being done one after the other. Usually people are okay with one outgoing and one return reservation. Anything more than that pisses people off because they might be worried about losing confirmed births while waiting. I have seen at least two instances in my life where the reservation clerk has succumbed to the pressure of the queue and refused to take a 3rd reservation slip from the same person.
Its...
more... probably better to have 2-3 people in the queue, each holding one reservation slip instead.