If you haven't studied either classical language previously (and hence do Course II) you don't necessarily need to study both in the main classics course either, as I understand in mods you would only study one of the languages (and texts from both, albeit the language not being studied in translation only). For the final honour school in Course II I believe the second classical language is optional (I would guess it's a popular option but not necessarily an obligatory one?).
I wouldn't consider the admissions statistics for the courses, particularly as CAAH is a much smaller course and therefore success rates are going to be much more sensitive to just a couple more students applying each year (or not). Also the average statistics presented for the main classics course include both Course I and Course II variants - Course I (for students who have done Latin and/or Greek to A-level) as I recall have a much higher success rate (as far fewer students are qualified to apply in the first place) and I believe for Course II (for those without either classical language to A-level) success rates are not that different from CAAH or ancient and modern history (AMH) or the other joint schools.
Just pick the course that is the best fit for your interests. Are you interested in archaeology/history specifically or were you also interested in philosophy/literature/philology etc? You may of course also want to consider other joint courses too (e.g. AMH for a broader historical view, perhaps particularly relevant/interesting if you're interested in late antiquity/the Byzantine period; classics and AMES where you can combine classics with e.g. Egyptology or Assyriology for example which may have some breadth of content of interest for archaeologically inclined individuals along with a lot of language background in both areas; or as more literature focused courses like classics and English/modern languages).