VG: Functionally (jams excluded), Ultra AC/5s are definitely superior overall to AC/10s in any kind of simulator due to greater range, lower weight and better rate of fire. But they do use up much more ammunition comparatively and lack the more powerful single hit of the AC/10.
UACs could be more expensive repair-wise, since even if your 'Mech isn't damaged per se, the weapons could jam more often than expected. But, MWO could do away with Ultras locking-up on the grounds that it never made any sense* (ever) but we will have to wait and see.
* The jam chance has long been considered by many to be an example of balance overkill.
Edited by Sychodemus, 08 July 2012 - 11:57 PM.