Liturgia Horarum or Breviarium Romanum? A case could be made either way. The LH has advantages. It was a good idea to make the Office of Readings something that could be flexibly disposed of at any time of day (the General Instruction actually allows it after Vespers of the day before); and so to make it less of a burden to those who are not required by monastic discipline to rise in the middle of the night. Prime clutter up the start of the day for a secular priest, suitable though it is for the monastic way of life. And Terce, Sext, and None can be difficult for those with a mobile lifestyle. Breviaries, even if small enough to cram into a pocket, are quite a weight to lug around. The old office was never perfect for the secular priest. This is shown by the fact that, de facto, he used to say it in amalgamated lumps, without any regard to the Authenticity of Time. And if you belonged to the right priestly associations, you even had faculties to say Lauds from midday the day before. The Office was regarded as a Legal Obligation To Be Fulfilled and not at all as the sanctifying of each hour by its proper Liturgy.
But LH has its very real and quite considerable disadvantages and difficulties. The main problem is the usual one: the Bugninides were never content to go for a minimalist organic evolution and improvement of what we inherited. Once they felt the wind in their sails, like all Committee-liturgists they couldn't stop just cramming in all the 'good ideas' that anybody round the table could dream up. So the psalms at Lauds and Vespers were reduced from five to two; contrary to the immemorial tradition of the Roman Rite, 'New Testament Canticles' were crammed in; those dreadful 1960s-style intercessions were confected.
Another case for using the LH is that S Pius X had already upset the immemorially ancient Roman distribution of the psalms; and Urban VIII had corrupted the texts of the Office Hymns (LH restores many of these in their original, ancient, texts).
I would only point out
(1) that it is legitimate to use the LH, but for Vespers on Sundays and Festivals, to say the BR. That is the one service which survived almost unchanged the redistribution of the psalter under Pius X. 1962 Sunday Vespers is the only surviving Office in an authorised form of the Roman Rite which S Benedict or Augustine, Anselm, Lanfranc, or Pole or S Edmund Campion, would comfortably recognise; and
(2) that the same is true of Sunday and Festival Lauds, if one is prepared to expand the S Pius X provision of psalms so as to include the three he missed out (see beneath).
The original Lauds psalms were (Vulgate numbering):
62+66 with one concluding Gloria Patri.
148+149+150 with one concluding Gloria Patri.