Wile studying grammar, I learned that the object pronoun could go in either of the places when the verb is being used as an infinitive. So, for "I want to buy it," both of these sentences would be grammatically and semantically correct:
1. Quiero comprarlo 2. Lo quiero comprar
Another example would be the sentence, "I'm preparing it":
1. Estoy preparándolo 2. Lo estoy preparando
But I am sure there must be some kind of preference in regular day-to-day speech. Which one of the two variations is more likely to be heard in which country (particularly keen on Mexican Spanish)?