I have found that they both have advantages and disadvantages...at least with my T-100 truck.
I had my SGII first and loved it...but it only displayed 4 gauges at any given time. It was easy to cycle through the gauges if I needed to since the buttons were on the front. The buttons on the UG are on the back and can make things a bit of a hassle if yer not used to it.
The UG easily shows more gauges at any given time vs the SGII. It didn't find my battery voltage though...so I have to have a separate gauge or git a splitter to hook up both the SGII and the UG at the same time.
I find the UG more responsive and will give you audible as well as visual warnings fer the alarm settings. These can be turned off, too!
The UG is not programmable by the user...so if it doesn't show when you scan yer system...it's not gonna show.
UG just lowered their return policy from 60 days to 30 days now...not sure what the SGII has fer their return policy.