Very different machines outside of the basic format (i.e. 3-motor, 3-head, 1/2" 8-track).
The 38 is a lot more sophisticated in its tape handling, and may look better on paper and sound more "clean".
Me personally I'd go for an 80-8 because I'm drawn to character and I suspect it has more color to its sonic character. I had a 3340S and loved how it sounded...I've never comared the amp circuits to see if they are similar to the 80-8 but I thought it sounded great.
Expect parts and help for the 80-8 to be orders of magnitude less than the 38. Many more 38s made than 80-8s. Also expect, in general, an 80-8 to be in need of more service/TLC/repair than the 38.
There are some of my opinions on pros and cons.
I HAVE NEVER OWNED OR OPERATED A 38 OR AN 80-8
YMMV, grain of salt, blahblahblah...