The arc view is way more useful than a 360 view. I really don't care too much about what is behind me on the route.
Arc.
As for the OP's
exact question, there really isn't enough information. Are you using a system where the HSI
and the nav display are selectable? What type of operations are you doing? What are you doing right now?
I can think of times where the 360 view is better, but there are far fewer of those than the "look ahead" arc. Then again, myself and the ones I quoted are in the business of going places.
If you are in another situation, the 360 might be better.
However, I will say with the information displayed on our archaic glass systems (and the "newer" style Primus Epic I used to use) I much preferred the ARC as the 360 view made all the symbology smaller, cluttered the screen with extra symbology and gave you less range for strategic planning.
The whole idea with glass is to
improve your SA, not replace it on a screen, and make you life easier and less cluttered providing the right information at the right time.
I guess we've come full-circle to the answer of your personal preferences and managing the information appropriately for the type of operation you are engaged in.