Second vote for ChaChaWan - often take clients there for lunch, but is a bit on the pricey side.
There is decent inexpensive Thai food to be had at stalls in Sheung Wan and Queen Street cooked food markets...
A bit out of the way but I really like Soi 18 in Causeway Bay and visit fairly regularly. Nice atmosphere and I have always enjoyed the food.
Not too expensive either.
That Chachathingy sounds good - but not for semi-regular lunch takeaways for 3-4 people on a weekend.
Have been contemplating the one in Sheung Wan wet market / food court - need to find some parking or waiting spots near it.
Thai Na on Second St.
Saw this one from the ex chef at Chachawan. Might try it... despite the fucked up review in the SCMP.
Gem:
Wan Chai newcomer Samsen – Thai noodles from former Chachawan chef | South China Morning PostPhat Thai noodles (HK$118) was the weakest of the three noodles dishes we tried. Perhaps it’s because it is very similar to Cantonese-style pan-fried beef with rice noodles, except here it’s made with prawns and kale.
Samsen is my favourite restaurant here at the moment.