I prefer High Khatun myself for arena as she has the speed aura and some additional TM control against the enemies.  For dungeons Apo may be better for survivability as he has a spot heal and a decent dungeon aura.

Thank you. Problem is only: her basic speed aura is only 19%, and most of legendary champs have more.

if ur going on a first turn basis, build a team that nukes, aka a TM boost into a aoe decrease att into a increase att into a big nuker such as ronda,. and u will win most of ur fights in about 10 seconds, nothing wrong with going down the route of sustaining but people normally put those builds as def lines, if farming medals etc in arena u usually want a quick fight.

I'm sorry, I'm a newer (German) player and I don't understand all of these shortcuts. Would you like to explain what you mean with 

- "aka a TM boost into a aoe decrease att into a increase att into a big nuker", - and also

- "put those builds as def lines"

I have Ronda, and Kael - my best fighters :).

TM Boost - A champion that boosts Turn Meter.  Used to push the slower members of your team ahead of the entire enemy team.  ( High Khatun, Apo, Arbiter, etc. )

AOE Decrease Defense - Area of Effect debuff that will drop the enemies defense by 30% or 60%.  Used to increase the damage that your nuker does.  ( Deacon, Warmaiden, etc )

AOE Increase Attack - Area or Effect buff that places a 25% or 50% to increase the damage your nuker does.  ( Spirithost, Arbiter, Seeker, etc )

Nuker - Your damage dealing champion built to kill the enemies, usually your starter champion in the early game.

short on skills summed it up well, as for the "put those as def lines" if u want to hold ur ranking in arena most people put a defence based team up, so that people avoid fighting them (defence based teams can be hard to nuke out so people go for the easier looking wins) and when ur attacking someone elses defence line you use an "nuke" method as described by shortonskills because its usually faster to farm ur daily medals.

if u do build a "nuke" team take in mind its important what order they go in otherwise it doesnt work any where near as well, which means the TM goes first, the increase att or decrease def goes 2nd/3rd and nuker which lets say in this case will be kael or ronda landing their aoe big dmg hits goes last and 1 hits everyone, aim to make ur TM booster as fast as possible so you have a higher chance of getting the first turn before the other guy, and make everyone elses speed line up in order so they go in order from there.

high khatun would be ur best bet as a newer player as ur arena lead / TM booster, as she gives everyone speed boost with her aura, and if u build her high speed she will TM boost on her first turn making everyone else on ur team be able to go next.

ur best nuker would be kael or ronda from what uv said, and as for ur aoe increase att/decrease def boosters im not sure what u have available.