Have read good reviews of both Seastar and Seatown. Both are equal walking distance from my hotel. At which one am I likely to get better quality and fresher fish and seafood?
Or should I skip both and go elsewhere in that same downtown area?
Both are very good, and either will provide you with top quality fish and seafood. My experience is that Seatown offers a slightly more casual setting, and has a bit more focus on shellfish, where Seastar, while not formal, is a bit fancier, and has more of a focus on (typically grilled) fish entree's.
Seatown is in the more interesting location, with the market right there, though that may be moot depending on when you plan to visit (market mostly closes as evening sets in).
Bottom line: Take a look at the menu's, see which one grabs your interest more. They're both going to give you great seafood.