Vasto Lorde is the name given to the strongest, most intelligent, human-sized group of Menos. The class below them is the adjuchas, who are mostly animals in appearance, and then below them are the giant towering godzilla things, called Gillian. An arrancar can be based on any of the menos classes, or just an individual hollow.
Of Aizen's arrancar, most of the grunts are based on individualized Gillian, the espada ranked 5 and below are all Adjuchas-based (except Arleri, who was a Gillian), Ulquiorra and presumably those above him are Vasto Lordes.
Oh, Wonderwice is also probably a Vasto Lorde. But he's wetawded, so he doesn't get to be an espada.