Frost is looking pretty good for Arenas if mostly manually controlled. I do a ton of 2 boxing and 3 boxing both arenas and BG's so 2 of the toons have to be basically full auto (sometimes I do dual screens with hotkeys swapping windows but it's pretty cumbersome). The auto-target I feel needs a lot more intelligence. Right now it's all or nothing, once any dmg decrease aura is detected (dispersion, bubble, etc.) the CR will immediately switch targets no matter how far or how high HP the next target is. If a spriest casts dispersion at 5% health and the hunter is a mile away full health, the bot will still try and go chase the hunter down while the almost dead target is running in the opposite direction to the pillar. DK's have about the worst mobility in the game atm and will never, ever catch any target that has already lost you. You obviously will never catch the hunter a mile away with 100% HP and the priest will never be touched again until he is full health pillar humping and healing. By the time dispersion is down and the bot detects it, you're already across the whole map trying to catch an uncatchable hunter at 100% health. Then once you are 8 yards from the hunter and you might actually catch him (still unlikely) disperson wears off and the CR goes back and tries to chase down the spriest that has already healed up half the way and is behind a pillar 30 yards away.
If you want auto-target to even half way work, there needs to be more than all or nothing based on something as simple as distance to next target and comparing health of each target. It's better the vast majority of the time to stay on an almost dead target with a dmg reduction aura if the next target is 40 yards away at 100% health.
If you want to get even more advanced for full auto, for BG's auto-target could easily be optimized by priority better using some type of multiplier to "change" the HP of the targets. If there is any dmg increase aura it means they are likely carrying a flag or orb (I know there is an option for CR to immediately kill flag carrier but it doesn't work) and take extra damage perhaps modify how the CR see's their health as 50%, if they are a healer maybe adjust it by 70%, something along these lines would make it much smarter on full auto.