Heroes that are really strong are ones that maximize use of titles, and minimize point gain by your enemies.
Titles: you want a damage base power on the team, esp someone who uses it really well. Fixer, Fanatic, Tempest, Ra, F6 Wraith, Guise, F6 AZ, Knyfe, they can all use it well.
I once used Immutus to gain Living Weapon on AZ, that was sick, as was Nightmist with Living Weapon.
One thing to remember is Guise can copy a base power, and if that base power is boosted by living weapon, all the better.
Chaos Lord is amazing, set yourself up to get it, a lot of heroes can get it, Ra, AZ, Adept, Knyfe, Nightmist, OX, etc.
Use your multi play cards wisely.
Unity is awesome for grabbing Stonejaw, put her late in team order and steal stonejaw with stealth bot for a good time.
For point denial Unity can be a double edged sword, stealth bot can single handedly dominate the match, but little bots award points to destroying gladiators.
Tachyon with synaptic and hypersonic is awesome, as are Haka and Fixer.
My top arena heroes:
1. Mr. Fixer: grease gun and living weapon make him dominant. DW Fixer can also be really strong.
2. Haka: Rampage, taiaha if you get +1, ground pound, pw haka is even better, because you can deny points like a boss with shielding, and healing allies is often better than haka of battle.
3. Fanatic: Fanatic can gain so many of the titles, and use them so well, and sacrifice actually shines here, letting you cut off points from many gladiators, zealous offense is wicked point denial, she can easily gain the damage taken titles, shes wicked.
4. Sky-Scraper: Monolith crushes point generation, and debilitator neuters warfang. Be careful what titles you earn, she can backfire in a bad way.
5. Expatriette: Her variety of damage is extremely usefull for point generation, and her ammo is amazing. Flak Jacket is best used to deny Warfang's big hit, a 2 point swing, and a well set up unload is a match winner. I've topped 20 points in one turn 4 times with DW Expat. Her synergy with Mr. Fixer and Sky-Scraper is even more crazy in the arena.
My favorite team for an arena stompfest is that list minus Haka, it is just unfair how dominant they can be.