If Jacky plays similiar like in VF5, then he is pretty much the best Character:
Keep in Mind, Sarah is ok In VF5, but nothing special, Jacky is Top 3 in VF, he doesn’t have + Frames on block like Sarah, but his other stuff is much much better:
Purely speculating, valid only if they don’t change him much from VF5 to DoA5:
-Jacky is the Sidestepkiller, Full circular High/Mid/Low, best and fastest Highcrushing Low Sweep
-Jacky has pretty much the best Strings, highly delayable, High/Mid/Low etc.
-Jacky is the King of true combos, most of his Launchers do require Counter hits, but they are safe on block. Half of your Life bar is easily gone in 1 Combo, better not whiff Holds vs. Jacky.
-Jacky can cancel many of his moves in SS or SSS, Slideshuffle and SideSideshuffle, so he is pretty much highly unpredictable.
So, safe Launchers, High Damage, unpredictable because of his ability to simply SS into Launcher/whatever, Jacky has all the stuff other characters, especially DoA-Characters, don’t have.
Heck, I bet he can even be played much more risky, the Rest of the DoA-Cast is lacking launchers, risk/reward in Jackys Favor, his SomerSault or Smash Upper on counter Hit reaaaaly hurt.