Extreme attack potions, extreme strength potions or overloads (A combination of all extreme potions in one) are the potions that would raise your attack and strength the most. You need around 88 herblore and 89 to make these extreme potions though (They aren't tradable and can't be assisted). If you don't have the herblore level for them then just buy super attack and super strengths as these are the second best.