abaddon's massive armour bonus is alot in low lvls. bt scorch's shield is in % and % scales upon lvl so at endgame it will hav higher %.. but abadon armour remains const. so at higher lvls it value degrades.
So sorch will absorb alot dmg in endgame then in low lvls but abaddon will absorb alot more then sorch in low lvls.

Conclusion:
at twink lvls choose abaddon
and at endame choose sorch