Well, Tohka is 660 Gigaton so I guess she has the AP advantage (meanless but still; I need to put the + on her profile)
About this battle, Mel has the advantage in versatility but Tohka can do some things which can give her the win.
I would say Meliodas wins. Tohka's best technique, Pavershlev, is practically useless thanks to Full Counter. Meliodas also has regeneration for his advantage and if things get difficult he can always beat her with Revenge Counter. Plus, Meliodas is a better fighter in terms of martial arts and swordsmanship.
SuperKamiNappa wrote: Demon Mark Mel scales from a 221.8 gigaton feat. If I'm understanding things right Assault Mode is at least 2x that, though considering he's High 6-C+ he would have to be at least 500 gigatons.
If you are referring to the values of power level in Nanatsu no Taizai, this is quite unreliable. For example, Late Morning Escanor is 114 000 in power level and Post-Revival Assault Mode Meliodas toyed with him while just being 142 000 so Meliodas' strength in Assault Mode isn't just doubled. Furthermore, Tohka is made of magic if i remember well so Meliodas can simply "Counter Vanish" her from existence.
My vote goes for Meliodas.