Perezoso vs. vago vs. haragán
The Spanish words 'perezoso', 'vago' and 'haragán' all refer to laziness or a lack of initiative. However, they differ slightly in their connotations and usage.
Perezoso
'Perezoso' generally describes a person who is slow or lacks energy. It can also be used to refer to someone who procrastinates or puts off doing things. This term has a somewhat more innocent connotation, akin to 'sluggish'.
Juan es muy perezoso, siempre se levanta tarde.
(Juan is very lazy, he always gets up late.)
Vago
'Vago' is a bit stronger than 'perezoso' and can denote both slothfulness and vagrancy. It typically describes someone who is unproductively idle. This term can have somewhat negative connotations, like 'loafer' in English.
Ella está sido muy vaga, no ha buscado trabajo en meses.
(She's been very lazy, she hasn't looked for a job in months.)
Haragán
'Haragán' carries a heavier connotation than both 'perezoso' and 'vago'. This term directly characterizes one as lazy in a sense of negligence and lack of responsibility – similar to ‘layabout’ or ‘good-for-nothing’ in English.
Mi vecino es un haragán, nunca cuida de su jardín.
(My neighbor is lazy, he never takes care of his garden.)
Summary
All these words denote laziness to different degrees. 'Perezoso' is more innocuous, denoting slowness or someone lacking in energy. 'Vago' points to purposeless idleness or loafing; while 'haragán', being the strongest among the three, refers to a dismissive attitude towards responsibilities.