All three are great for a wide range of purposes.

For racing, I would want nothing less than STI shifters. There is no way I would be able to climb hills during races if I had to reach down for a down-tube shift. Being able to shift when pounding out of the saddle really makes STI's worth it.

For regular recreational riding I think down tube shifters are perfect, and if you don't like reaching all the way down or want to do some touring, use bar-ends.

Again I think its all about the application. Are you going to need maximum efficiency and performance when riding? Or is that not a necessity?