>> Which SIM card would be the best in terms of value & quality for an extended period (a few months)?

Unless you have a HKID card or are willing to put up 3000HKD for deposit, you are limited to prepaid, which have been discussed at length.

A more recent addition is China Mobile 4G/3G prepaid. Only Chinese website available.

http://www.hk.chinamobile.com/tc/pre...ices-4g3g.html

SIM cards are often sold at 1/2 price or less at Apliu St., Shamshuipo if you have time.