For the average player I'd guess it looks something like this:
DMM:
+ haven't witnessed a single bug on it
+ lots of gifts for playing the game and generous compensations when something occasionaly goes wrong
+ way more content than the Nutaku version
- in japanese
- the gacha rolls tend to be unlucky
- the auto run system during missions requires the player to click the continue button if a fight occured this round
- censored scenes
Nutaku:
+ in english
+ lately the odds of getting good gacha rolls tend to be higher
+ the auto run system during missions is fully automatic
+ uncensored
- slow implementation of DMM content
- changes to the original version were introduced which are unnecessary/unusable
- hardly any useful gifts/compensations
- unfortunately bugs tend to appear after updates which take time to fix
- translations have slight errors/inconsistencies
A lot of these depend on the player of course.
For people who understand japanese (in my case about 95% from hearing, about 50% from reading - more once I actually translate the kanji I haven't learned yet) the language barrier is not that significant and I'd recommend the DMM version, as it additionally is more stable.
For those who want to know exactly what they're reading and are not bothered by imperfections, I'd recommend the Nutaku version, as it additionally has better odds at gacha rolls (unofficially).
Name: Volarmis
DMM ID: 317568967