Definitely ATPL, if only to save you time! To achieve a CPL/IR you need passes in either the 14 ATPL exams or the 9 CPL exams and the 9 IR exams. You get no concessions, even on Human Performance which is the same exam in both sets of 9!
Your ATPL exams will only be valid as such for 5 years (from the final pass), but if you intend to do an IR in this time this is the way to go. Then if you can complete the right breakdown of 1500 hours you will have an ATPL, if not you keep the CPL/IR saving 4 exams.
I have taught students older than you for the ATPL exams!