If I was conflicted on this as you are I would take the whole question to my spiritual director and ask him/her and not settle for “you pick”.
Well, as Benedictine oblates it is for us to pick. Our oblate statutes state that we are to pray the Liturgy of the Hours as our condition in life permits. Some abbeys tend to be specific, ours isn’t but “suggests” Lauds, Vespers and Compline and even produces a condensed breviary for oblates to use, using the same psalm schema as the monks. The suggestion thus appears clear, to me at least. I consider myself blessed that I can pray all of the Monastic Liturgy of the Hours as our abbey prays with one small exception, I spread Vigils over two weeks as allowed by the GILH of the Monastic breviary I use.
Now, the GILH (Monastic version) in our “official” monastic breviary states that those engaged in external apostolates, and those traveling, can licitly use the 4-week LOTH. Secular oblates by their nature are engaged in a sort of “external apostolate” in that we are to live the spirit of the Rule in secular life (btw we have a couple of priests who are also oblates, and the Holy Father is rumoured to be an oblate himself).
It took me a lot of experimentation to find my own balance. At the lighter end, the 4-week LOTH, and at the heavier end, the original Benedictine schema which is still licit. I finally settled on what my community does with the exception noted above, and if I am on an extended trip, I will revert to the 4-week LOTH because it’s all self-contained in one book, and easier. If my life circumstances should change, I will reconsider my options.
My guess is that his spiritual director will not pick for him. He will most likely offer suggestions for him to try, but will leave the choice to the oblate. My suggestions it to not sweat it or obsess over it, and experiment. Anybody who regularly attends liturgy at a Benedictine abbey, and pays attention, will notice over time that the monks experiment with their liturgy (although some changes are subtle and you have to be aware). I’ve been an oblate for nearly 9 years (10 if you include my formation year) and it wasn’t really until this year that I figure I’ve found a nice balance.