I guess this is why adcomms are made up of different groups of people.
Here's my logic behind choosing the 3.5/38 as more impressive: the person with the 3.5/38 has shown they're consistently average/above average for a medical school matriculant, as far as their GPA goes. they can hold their own in the classroom. their MCAT backs that up, showing they're a good test taker and/or learned the material well. they'll probably be good in class.
the 3.9/30 has a discrepancy somewhere. the 30 means they're about average for a matriculant, maybe on the low side, which makes me think they either didn't learn material well or can't take tests well. if those two are true, though, how'd they get a 3.9? was their undergraduate school too easy? if so, what would it have been at a normal school? 3.5? if their undergraduate school was normal/hard, what's with the 30? do they have good days/bad days? do they fail to prepare adequately for big tests (USMLE)? are they only good at material if it's given to them slowly, over a semester? are they bad at applying knowledge? can they not store information for long?
I dunno, just my thought process 🙂