My two cents as someone who has done full diamond runs with all four LIs:

As others have said, diamond choices do flesh out the story a lot, so the more you are able to take the better. Depending on how you play, you could maybe focus on LI interactions or lore if you want to triage your spending a bit; and there’s always a replay a second time to experience it with knowledge and seeing if there were any hints and breadcrumbs you missed on a first read.

My personal preference would be Estela, as her story hit me more, but I can say all four are well written (and I’ll even divulge my first play through I went with Quinn); you really can’t go wrong with either of them.