Cell
70877
1491751
17401
410

Buu
70877
1413364
12548
419
__________________
Cell
0
78387
4853 = 3.5% Damage mitigation
-9
__________________

50% Silence for 1 turn, 3 Targets
15% Teleport, Once a turn (full damage mitigation)
50% Heal once per battle
12% Dodge, Restore 35% Energy increasing Silence consistancy

Taunt for 1 turn forcing default attack
15% Teleport, Once a turn (full damage mitigation)
30% Block, 20% Chance to Chocolate for 1 turn. Applies Once each 2 turns.
30% HP Revive once per battle.

=Active=
Cell: Minimum 0% Damage mitigation, on average, 1.0 (conservative damage mitigation value of 1) equals a 50% Damage mitigation from 1 target. Up to 150% Or 1.5 Character damage mitigation.
Kid Buu: Garunteed 50% Damage mitigation.
====== Result ======

Cell, having a significantly high damage mitigation potential while also having the ability to delay healing or bleed detonations.

=Passive 1=
Cell: 15% Teleport.
Buu: 15% Teleport.
====== Result ======

Tie, Easy one here.

=Passive 2=
Cell: 50% Heal once per battle
Buu: 30% Revive once per battle. (drops all buffs/debuffs)
====== Result ======

Tie, while the effective regain is significantly less, being able to drop all debuffs or bleed stacks makes up for that 20% life descrepincy.

=Passive 3=
Cell: 12% Dodge, Restore 35% Energy limit to 5 times a round.
Buu: 30% Block, 20% chance to Chocolate for 1 turn, Once every 2 rounds.
====== Result ======

Base block mitigation is 30% damage, With 30% chance for it to occur giving it a 9.0% Damage mitigation value for an entire characters life time. 20% Chance to choco for 1 turn, Every 2 turns on block. With a 30% block and only a 20% of it happening on block. You are left with only a 6% chance of it occuring per attack, or 30% Chance of it occuring in a full turn cycle. Assuming your tank on average lives 5 rounds (personal average) That means its likely to occur once through the entire combat. Resulting in 15x5= 75 theoretical attacks without convergence. Causing a 1/75th damage mitigation equating to 1.25% damage mitigation. So 9.0% + 1.25% = 10.25% Damage mitigation. Vs's Cells 12% Flat dodge and none of this takes into account his 35% Energy gain on dodge causing a potential high ceiling of silences effecting heals, bleeds, detonates.

Conclusion: Cell through passives has a 25% + 1.75 higher situational damage reduction and a 3.5% static damage reduction. Combined with his higher base HP, statistically, he has the highest damage mitigation between the two.