Speed, Speed, Speed (updated article 18-oct-2016)

At the time of this update, speed bonuses are what defines your arena rank.
Using the same team/gear, if you're faster, you'll most probably win. (To get faster, you'll need good Mods, that's another subject).
Let's face it, there's some luck involved. Dodges, Resists, etc can alter your results. But if you take the time to inspect mods equipped by the top 10 or your server, you'll notice the trend too.

I won't detail how it works here. In short: the best value will go first. But you may want to try things, check if a mod update is interesting, etc.
The tool below will help you simulate turn order for any squad composition you wish to try. Just report the speed value of your team (and if you wish your enemy), and take a look at what will happen.

Disclaimer : It's not possible to take into account turn meter gains or loss. Thus sometimes the order will not be the same.
However, with flat values and no modification, the results should be accurate.

The simulator

Report your squad's values in this little tool, adjust, experiment...

The dices ? They mean the RNG will decide... If two or more characters are supposed to take a turn at the same time : the order's random.

Be careful : This simulation does not take into account turn meter manipulation.

• Ex 1: A droid squad boosted by the Jawa Engineer will see different results in game. The jawa will fill every other squad member's turn meter with an ability ; then HK-47's leader ability fills each droids' turn meter for each critical hit)
• Ex 2: Qui-Gon Jinn goes first, and manages to reduce an ennemy's turn meter with his basic attack : the damaged character will play after what this simulator calculates.

This work is based on the community's discoveries. I just applied what I found, and it may be prone to errors. Feel free to leave your remarks below !