Who's Stronger Alaric vs Marcel?

A bite with potent enough werewolf venom that was so potent that it could kill even the likes of an original. Alaric had no such ability. Marcel had the abilities of an Original but with a much greater degree (probably stronger than Alaric).

Is Alaric the strongest vampire?

Esther's spell decreed that Alaric would be stronger than all her children (including Klaus), so it wouldn't have mattered if Klaus was at full power, Alaric would have always been more powerful. Sadly the spell only made him stronger than most of her children.

Is Marcel the strongest vampire?

The Originals focuses on the first family of virtually indestructible vampires, but Marcel Gerard is the strongest vampire on the series.