使用http.TimeoutHandler还是ReadTimeout / WriteTimeout？

These two deal with different aspects of http request/response lifecycle.

http.TimeoutHandler is used to limit execution time of the http.Handler. it will return 503 status code to the client, if http.Handler doesn't finish in stipulated time.

While, ReadTimeout and WriteTimeout deals with network I/O timeout, i.e time required to read/write request/response body to your client respectively.

So, http.TimeoutHandler handles the case where your handler (code block that handles http request) need to be complete in set amount of time, by wrapping your original handler. while http.WriteTimeout or http.ReadTimeout is used when you dont want to wait for network read/write of request/response indefinitely.

If you are going to expose your app naked (directly) no HAproxy/Nginx in front, changing the defaults may help, for example (fine-tune them based on your requirements):

// configure server
srv := &http.Server{
    Addr:           ":8080",
    Handler:        router,
    ReadTimeout:    5 * time.Second,
    WriteTimeout:   7 * time.Second,
    MaxHeaderBytes: 1 << 20,
}
log.Fatal(srv.ListenAndServe())

Here is a very nice article explaining more about the topic: https://blog.cloudflare.com/the-complete-guide-to-golang-net-http-timeouts/

This blog article does a good job of explaining, but essentially they fulfil slightly different roles, as demonstrated here:

Link to blog article

You've not included what your usecase is, but hopefully this is enough information to be able to make a decision.