The older series Mini-30s are the same as the 187-up Mini-14 Ranch Rifles, IIRC. Flip-up rear aperture sight, integrated scope mounts, and "pencil barrel." AFAIK
, Ruger never made a "Standard" (hump rear sight, w/o scope mounts) Mini-30, they were all Ranch Rifles.
The newer (580/581) Mini-30s got the same upgrades/improvements as the Mini-14s. Namely, a thicker barrel and more robust sights front and rear.
All are great rifles. Accuracy may be better on a 581 series, but there are products out there that will help rein it in (if it's even an issue for you). Like all Minis, some rifles are good out of the box, and some shoot patterns rather than groups.