I saw this question on TGP. The different routings between the two algos are among the main features that make them unique. Here are some informative, interactive links for ModEchoVerb & Spacetime. I added a link to a forum post to illustrate SpaceTime’s PEDAL VIEW, which makes it very easy to see the FX routing paths. ModEchoVerb routing is a bit more mysterious, but you can figure it out from the MEV link below.
Subjectively, I use SpaceTime more now. Maybe because it’s newer. The modulation section alone is a wonderful variation on standard fare. ModEchoVerb’s mod definitely has its applications … more random in nature. One circular delay routing around the whole MEV, vs. independent delay lines in ST.
The delay algorithms are all different, in what they expose as additional parameters. That makes it easy to customize your presets, based on the feature set presented, or sound results desired.
I’d put them in two main categories: Delay Time pitchshifts [Vintage; Tape; etc.], and Delay Time crossfades [Digital, etc.]. You can easily determine that (even in a 5-minute algorithm preview) by turning the Delay knobs with something in the delay buffer. One algo may offer more extensive EQ, or ducking, or multi-taps; all of the modulation variations are uniquely configured per-algo.
Having had the PitchFactor long before any H9’s, I’d consider the majority of the Pitch algos to contain “digital” delay features. Pristine, until you start mangling them with inline pitch or modulation regeneration.