Having owned and used both an SS UV26 and a DiveXtras Sierra, I have to recommend them both.
I sold the Sierra, though. Why? Couldn't afford a Lithium battery, and the nimh battery wasn't enough burn time for technical cave dives. The 26, at...more than double, but I don't think quite three times the weight, felt much stronger and faster in the water.
Both use the same shaft seal, and I don't believe the extra oring from the nose cone is really a problem, as much as Dive X will tout their reduced oring count. I'm not a fan of the welded on shroud struts, but I don't think they are a problem, either. The SS has "hollowed" bolted on shroud struts. Drop the scooter, bend a strut, you can get a new one for real cheap and you are fine. Do that on a Dive X and you have to bend it back, and hope the weld doesn't develop a leak, which it probably won't, but still...
My next scooter will probably be one of the lithium SS's, but if I ended up with a lithum Dive Xtras, I'd probably be just as satisfied. The weight of a UV26 is really a dive killer, in the sense that I don't carry it very often due to the weight. The Sierra, I took diving much more frequently.
I can't compare the Sierra to the Suex, but I haven't heard any complaints about either. To me, it depends on what your buddies dive. Here, most people use SS or Gavin, which use the same prop, and similar motors, if a buddy has a Gavin that breaks, I can probably diagnose the problem and fix it. If your buddies have Sierras, then get a Sierra so you can share spares kits. If they have Suex's, get that so you can share spares.