Been looking up these forums for information on tailoring, and finally made a few orders, so I thought I'd put my experience down for anybody else in a similar situation in the future.
I've had 2 shirts made from WW Chan, and 4 from Jantzen, then 5 more, then 5 more, then 5 more. I went a bit overboard. Suffice to say, I was very happy with Jantzen. I am new to more sophisticated fashion, but I do have a decent eye for style and attention. WW Chan's (and presumably Ascot's) is better, but I think unless the price is of little issue to you, it is clear to me that Jantzen is a far better choice. Certainly if it is reasonable for your financial situation to buy a large number of shirts at the higher range, then it might be best, but from my semi-untrained eye, the difference is fairly minimal. WW Chan's shirts were just... good. Like no mistake they were good, but it was beyond my budget to splurge on a dozen shirts with them. It is my opinion that having a larger variety of very good quality shirts in a wardrobe is better than having a few slightly even better shirts. The quality seems unbelievable to me considering how much cheaper it is.
I will admit that there are some areas, such as the buttonholes where there are loose strands, but for the most part they are very good, and the problems were easily fixed. Considering the price, they'd have to be several times less durable for that to even be a huge issue.
I think a good part of the negative experiences of other people with Jantzen is from the mail order aspect of it. Being in the shop personally and able to discuss alterations and styles, and finally to choose fabrics probably made it a far better experience for me with Jantzen than a lot of other people. I spent quite a lot of time looking for the fabrics I wanted so that worked out very well. The fit is extremely good, construction is good, although I've only worn them about 10 times. Having control over the style was also extremely useful. It might have helped that I spoke Cantonese and, as a recurring customer, the staff put effort discussing styles, fabrics, and giving me their input, but my experience was very positive.
I've also had a suit made at WW Chan, and I think it's great. I plan on having another made next trip. As a side note I've also had suits made at Simpson Sin (a budget choice, but very good for the cost), and they were good for the price as well. In making these observations, I've also made comparison to a couple of other tailors in Hong Kong, and compared some of the shirts they had on display, and generally I'd say these are the three tailors that stood out to me in terms of quality and value for money. I've also enjoyed the tailoring experience with all of them.
I'm considering making a post about my purchases with picture, but I'm new to these forums so I might lurk a bit more in case I get flamed or something, but if anyone would like something like that I'll try to get that done.