Sorry if this has been discussed before, or if its common knowledge. I'm just getting into 300blk with a 9" pistol. I see the lighter 124gr rounds and then 150-ish grain rounds, and then the heavy subs. When would/should i prefer one weight over the other? Does the 124gr have any advantages over the 150gr, or vice versa? Subs seem fun because they are so quiet, but seem to have some poor terminal ballistics. I want to start stocking up on it, with sme being SD ammo and a large portion for plinking.

I haven't hunted in years, but I keep a pile of supers. You said subs have bad ballistics, I think of it as limited capabilities. Like 45acp. Fat and slow but really quiet. Even more quiet in a bolt gun.

110gr to 125gr range is best for supers.  Avoid the 150gr stuff except for range time.

Subs are subs.

110gr Barnes Tac-tx
110gr Hornady Vmax
110gr Nosler Varmageddon
110gr AAC Sabre Black Tip
115gr Lehigh Controlled Chaos
120gr Sig HT/SBR
120gr Barnes Tac-tx (Some like this over the 110's for hunting out of longer barrels)
125gr Nosler Ballistic Tip
125gr Hornady SST

There might be one or two more I forgot, but for a 9", the the first few listed are the way to go.