You can usually tell where on the spectrum it falls with the balanced modulator choice. Quadrant multipler vca chips (ad633, that one fancy ic I can't remember the name 2653?...mostly eurorack), 1496 ic (maestro, classic stuff), diode ring are usually pretty good ring mods.
The stuff using 4000 series logic, comparator ics, and plls are usually noise makers (side effects bug I assume, .holowon, seppuku, motormatic and I think outer rings).
There are some dual VCA op amp based ones (fonitronik), tube (metasonix), and transistor (buchla 100, Carlin...usually bad rejection) that are somewhere in the middle, but not too common (kinda like fast switches usually).
Of course, if you start getting wild with the carrier, any thing can be noisy. But it's usually that way for pedals and euro
Diode ring tend to be pretty smooth and musical no matter what you throw at em (monobius, DBA, ring stinger).
Usually, the controls are pretty telling to me.