The difference lies in the interface. While I generally prefer a
tracker, a sequencer is good for fluid sounding recorded parts, or for
people who are used to traditional music notation. It's not really a
question of when, but a question of which kind of program you prefer.
If you like to input notes live with a MIDI keyboards, you will likely
prefer a sequencer. If not, you may want to give Renoise a try.
Renoise also has a very capable sampler integrated into it.
> Ok, so the question must be: