Im in the same position as you. I have just got a 2 yr old and to help me I have bought 2 books. from birth to backing and basic training of a young horse.
In the birth to backing book it states that lungeing a horse is fine as a form of exercise and to teach the horse balance and obedience to the voice and whip but it does not introduce a horse to the all-important feel of the riders hands on the other end of each rein, nor does it teach him to accept their guidance. nor does it imitate the effect of the outside leg in the same way as long reining. Furthermore, lungeing may confuse the horse if you have spent weeks teaching him that when he stops and turns in and comes up to you, you punish him being sending him away with a whip, which will confuse him and spoil any degree of join up you may have achieved.
So after that what do you think?
Im going to get my mate to help me long rein my boy first.
I say long rein, as you say when else do you work a horse of one rein. You can long line off the side rings of a cavason if you want to save mouths if you don't trust you hands with a baby. Lunging also causes uneven loading of limbs and head tilting, not great in an older horse let alone a baby. Like everything it has its place but i much prefer longreining and its much more versitile, pole work/ taking them out and about wise
i think to loose lunge first to get him moving forward so he has only got himself to fall out with and not you then i would long rain him so he has the best chane to develop and walking out stright will then just become the norm for him and when you start to back him his is already uesed to having some one behined him and the contact with the bit
we always started our young soon to be racehorses with lungeing 1st, then went onto long reining. we got them used to 1 rein before introducing 2 reins. we'd only lunge for a week or so depending on how quickly they settled into it. then progressed to a 2nd rein for lungeing, then onto hacking out with the long reins.
all ours were fab to back (except 1, there's always 1!), fab in traffic, hacked out alone no probs and were generally wonderful.