In order of preference:
I) Nemesis II on the MSX , best MSX shmup, and maybe best shmup ever.
II) Raiden, Arcade, best arcade shmup i have played.
III) Soldier Blade, best pcengine shmup, best music in any shmup.
and best shmups on the amiga, as i tried them all, is Battle squadron, then hybris, then SWIV.
NeoGeo, for me it's last resort.
Pc dos, i can't recall any good one.