Long throated 30-06, 284 winchester/shehane or 280 ai for a 18-20" suppressed long action.

[Montucky Roamer]

I'd be wanting to do 280 ai throated for 180 eld, absolute wind cheater.
Also, the 30-06 ai, built around berger 185 juggernaut. Killer set ups to 700 easy. But I'd do the 7mm version myself.

 

[cajun]

280ai. Thats where I'm at.

 

[Plinker147]

I believe I would do the 284. It's a great round, "first short mag"can't go wrong with it. But I think the 30-06 might give the best performance in a short barrel. Really splitting hairs between the 3, they will all be real close in that platform

 

[FEENIX]

I'm a dirty sl*t for lapua brass and am struggling with analysis paralysis. Bore volume vs short fat powder columns vs no trimming. Have a defiance long action so trying to milk performance. Help.

This boils down to personal preference/intended purpose. "I" prefer .30 cal over .28 cal, between your choices, I'd go with the venerable .30-06. If you trying maximize performance, you might want to consider the .30 Gibbs. I have a Kimber 84L Hunter 24" in .30-06 that I had my gunsmith re-chamber ti .30 Gibbs; it's propelling the 190 Berger VLD at 2806 FPS with plenty more room to spare and I am only using powders that I already have open. Good luck!