What is the best treatment for hypertension in er?

Too general. The question is too non-specific. There are multiple ways to treat hypertension and dependent on how high a BP and the other circumstances existing, the treatment is different. Sometimes, lowering the BP too much is not even a good idea (like in a stroke patient).
Many options. Depends on patient type, associated medical conditions, severity, symptoms, heart rate etc. Malignant hypertension is associated with symptoms such as chest pain, shortness of breath, blurring of vision and confusion. It is a medical emergency treated with intravenous medications such as nitroglycerine, nitroprusside, furosemide, labetolol, hydralazine, Esmolol to name a few.