Well I mulled this over for days in a previous forum and the awnser is Brolly NO Question.
Cell was defeated by Gohan with battle damage (draining his power) JUST AFTER reatching SSJ2.
Later in Movie 11 (Or is it 10?) Brolly comes back defeats (NO CONTEST) Adult Gohan SSJ2 who has far surpassed his child self in power.
Brolys power is bordering on SSJ3 with that might.
I do realise Broly can't regenerate but , when he used a attack witch destroyed a etire island in one shot , Cell wouldn't have alot of chance.
As far as I know
Chance to win
Cell: 30%
Broly: 70%
Even if sell pulled his own UUSJ trick , Broly would then be faster.
Saiyan X
saiyan2k1
the obvious choice is of course broly!!!because he has all that power!!
Like I said before, power isn't everything. Remember when Trunks fought Cell in his ultra SSj form?
The point my good man is that , When Broly goes USSJ , he skips USSJ and goes to his own more powerful custom transformation , fan dubbed "LSSJ" and GAINS speed , doesn't loose it. He also gets taller and much more reistant to damage... He walked through a fully charged Kamehame and LAUGHED... When Cell did that he got his head blown off and various limbs...
Power isn't everything , Power speed brains and ruthlessness.
Cell wins on Brainpower but in Power and Speed , Broly wins hands down.