As far as I know, HKU JD is the best in terms of reputation and job prospects, followed by CUHK, with CityU being a distant third. Law firms in HK have certain quota for each school, CityU is therefore kinda "discriminated" as there are fewer seats reserved for their grads.
But if you do well at CityU you will be able to get into PCLL, which makes you able to practice as a lawyer. Do keep in mind because of the reason I mentioned above, you need to be (very) top to get a TC from a city firm.
Since you are planning to enroll in 2018 I suggest you to apply CUHK as well. Their entry requirements are just a little higher than CityU, so if you can get into CityU you have a chance for CUHK.
Well, in fact, if you have your PRC bar under your belt you might probably find yourself in a relatively advantageous position when applying for jobs before the PCLL.
However, for most Chinese students, probably the only thing that stops them from winning a training at one of those international firms is language and the cultural fit. Otherwise, provided that you have an excellent/respectable command of English, most firms should be happy to take you onboard.
That aside, I would say, the best strategy is to apply for CUHK JD if you can (which should not be that difficult if you could polish up your CV and PS - they do have a record of taking up less qualified candidates to be honest), so that at least you can be on par with them rather than being crowded out as a CityU JD.