The analysis of high-resolution H-alpha and white-light observations on the emergence of 73 active regions shows an intrinsically different behavior for both the large and small ones. The small active regions (magnetic flux of approximately 5 x 10 to the 21st Mx) display circular structures of supergranular size with pores only at the borders, whereas the large active regions show elongated structures with pores which develop at the center and later migrate towards the extremes. These observations are used to suggest two different models for the emergence of these two kinds of active regions: the small ones are produced by the superficial convective concentration of loosely packed flux and the large ones are the result of tightly wound flux ropes.