I would also have a look at how useful each will be from an international perspective. I suspect the ACA travels better if in future you want to work abroad.
If it were me I would keep my options open longer and do ACA, CTA is always possible post ACA if you want to specialise in tax. (From a personal perspective audit always bored me and I found tax interesting, but you need to be looking to your whole career not just the first ten years.)