Template vs hook for views filed output
as per the various articles, its not good to have too much templates in drupal.


With respect, and depending on exactly what you mean by "too much", that's pretty much nonsense. If we're talking about 10,000 template files on an uncached site, then yeah, you would probably have problems. But those problems would be with your application's design; in the real world, with a normal application, that statement is just untrue.


  which approach is good and loads fast ?


Both are 'good' (or 'bad'), depending on your point of view, and how well you write the code for them; differences in load times will be negligible, especially with caching. If you're really worried about micro-optimising, then you need to benchmark your site, while it's under load and sitting on production hardware; that's the only way you'll know which method is faster for your use case.

It's not possible to give a blanket "this way is quicker" statement, because it depends on what the rest of the site is doing, how you have it and the server configured, and how good your code is. Always test in the real world rather than ask for others' experiences - you have no way to know if their experiences actually apply to your scenario.