The question of which is easier is hotly debated on other MN boards so I guess it is not clear-cut. Or maybe it depends on the particular subject. IGCSEs are certainly widely recognised and are what most private schools do, so you shouldn't have any trouble at all with college entry or employers' requirements.
The main reason IGCSEs are so popular with HE kids is that there is no controlled assessment, just exams, so there is less hassle and expense arranging them.
Here's a wiki with a link to a busy email list which you may find useful: www.nwilts-he.org.uk/he_exams_wiki/