Agreed on Openrice. I think in terms of good budget places, it's probably easier to just find something on Openrice depending on where you are staying/where you will be that day. Generally, there's at least a few decent places in each neighborhood. And I don't think its worth travelling a long ways for a bowl of noodles.

Din Tai Fung, in my opinion, is not as good here as it is in Taiwan.

I don't have any particular suggests for high end places, but if you find yourself in the areas more well-known for food, exploring (and searching on Openrice) and trying a few places might be an alternative to splurging on just one meal. You'll get to see more of the neighborhood and what locals here eat.

On the Island, Tai Hang, Wanchai (on the streets between Johnston Road and Queens Road E), Shau Kei Wan (for cheap local food), North Point/Fortress Hill (Shanghainese/other Guangdong foods), Tin Hau (on Electric Road, desserts). In Kowloon, Kowloon City (for Southeast Asian foods), Jordan (local food), MK (street food, I guess, thought I don't like it), Hung Hom (lots of small cheap eats).