Speedwise (generally) the fastest to slowest are:

display list
vertex array
immediate mode

This assumes you''re doing more than just a few vertices. If you''re only drawing one quad or a few triangles, immediate mode may be the most convenient choice.

As for your second question, if you''re just testing, do whatever works--at that stage of the game (pardon the pun) you''re not looking for speed yet, just functionality.

Display lists only take you so far though. That list should look like:

ARB_vertex_buffer_object
display list
vertex array
immediate mode