CX-300 is very similar in performance to the Creative EP630 IMO, and to me EP630 is more worth purchasing as compared to the CX-300, and it should be cheaper as well (at least it is locally). The CX-300 also (to my ears) has the treble as shrill as that of the EX71 IMHO.
Compared to the EX71... well, personally, I think the EX71 is rubbish for its price, and its performance isn't very stellar compared to normal earbuds as well. The EP630 trounces it flat by being more controlled yet just as strong in the bass, and is more detailed (same goes for the CX-300 VS the EX71, but CX-300's treble isn't much to speak of IMHO).
In the end, I'd recommend the EP630.