I believe you want 1:1 buck to doe in a perfect situation.
You want your best genes breeding.
If you had a spike, a fork, a 6 and an 8 walk in and they were all 1.5yo, I'd take the smallest.
Guys around here will shoot a 10pt 2.5yo all day long, what you leave are 8pt and 6pt 2.5yo to breed...
whether or not you can really influence your area is another argument.
There's probably a paper to prove anything you want out there on the internet...
but some things I've read suggest that say at 2.5 a buck main frame will be present... 8pts , 9pts, 10pts, etc... We have pics from a 9pt at 2.5, 3.5, 4.5... he got bigger, but same frame essentially his g4s were always week, read up online at all the research you can. but essentially I'm a believer in taking out weaker genetics as early as recognizable. I think by 2.5yo you have a solid idea... at 1.5 it would be hard to say.
But like one thing I read, was, no deer breeders are buying forks or spikes at 1.5yo when they can buy 8pt, 10pts...
So it makes sense to me if 2 spikes were to come in, it would make more sense to shoot the small of the 2, and so on...
around here a 3.5yo is starting to really get big compared to 2.5yo.
good luck!