I have both and they both quite good i think.
The Mauler is slower but seems to hold more firepower, in particular i use the MX90. Its tough but with support can really throw out damage. I usually take this on the MX90.
http://mwo.smurfy-ne...471651c53a80079
2x LB10X, 1x PPC on one side and 1x SRM6, 3x MG, 1x SL. Good at all ranges, takes some getting used to however with support it does more damage the closer you get great for pushes
The Zeus is also quite tough especially the 5S,and is also good at zombieing if you use STD engines. Also will move faster than most assaults ive used and can do decent damage, but not as much as most heavier assaults. I have been using the 6S like this.
http://mwo.smurfy-ne...7a8a3ff1449f466
1x AC2, 1x Gauss rifle, 4x ML. a little light on firepower, but the ac2 helps throw off the opponents aim while the Gauss cools down and the MLs with modules are great for close defence, plus with the STD 320 it moves at 69kph so its fast for an assault.
As for load out, the Zeus is better for energy weapons i find, more hardpoints and some useful quirks.
Ballistics will generally be better on the Mauler, and missiles work well on both.
Hit boxes are by far better on the Zeus, quite easy to protect the CT. Mauler is really big and wide and the CT gets dropped often.
I like both for different roles, hopefully this helps you