Halo had two of the best, the charged plasma pistol and the scoped magnum. The scope on the magnum was actually useful and you could complete large sections if you were good with it. In multiplayer you could snipe from miles away if you had some skill.
The plasma pistol on the other hand was perfect for combos. The weapon balance in Halo was amazing. You hit shielded enemies with the charged plasma pistol to lower them then quick swapped to your other weapon and finished them off. Gaming nirvana.