Pop-Up or Conveyor?
Whether you need a pop up or conveyor model depends on volume, available counterspace and what exactly will be cooked with the toaster. If all you'll be cooking is bread and bagels, then a pop up will suffice. If you intend to cook open faced sandwiches, thicker breads that won't fit in the pop up models, or breads with oil or cheese on or in them, a conveyor toaster is the way to go.
Which one makes better toast?
Either one can make perfectly adequate toast, although pop-up toasters can be a little more controllable, usually having some form of light/dark selector knob where you can control exactly how long toast is in the toaster and how dark it gets. This can be slightly more difficult to adjust properly on a conveyor model.