We've never tried any, but I'll bump this for you again. Maybe one of the guys who has reviewed a few toys like this will wander over with an opinion.
In the meantime, I took a look at the specs and reviews. Take my advice with a grain of salt, because we've never tried these or any other realistic pussy-and-ass sets.
They're the same material, both vibrate, they look like they're similarly sized. Cassidey's the only one with a verified review, and it's very positive. It sounds like they both have 2 separate tunnels; Czechmate's review mentions that they are very different, and doesn't note any fragility issues, while the Lexa doesn't say whether they're the same or not, but a customer review mentions issues with ripping. If I were the one buying, right now, I'd probably go with the Cassidey. (But I'm biased... I almost never buy anything that doesn't have positive verified reviews!)