shtml I think they say that the form with "should" is the most general one, the form with the infinitive is the most formal, and the form with the simple present is the most informal (so all of them are acceptable). That comes from the BBC Learning English service though, so it's definitely about UK English (as far as I know, in America the most common option is the infinitive).
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RuslanaCan you please check whether my assumptions are correct?Your observations are all right on the money as far as I'm concerned.