Hi, Amy!
Welcome to GTER.
My suggestion is that you should tell us more about you.
CET4 is a illegibility concept to describe your English level.
I think you may need an intensive training, but I'm not familiar with the centers in BeiJing, you may ask other guys.
Feel free to ask us for more details.
I took part in global training center for intensive study. It told me what the IELTS is,
but if you hope to enhance your English score only by it, I do not recommend any
one you mentioned above. If you want to know the skill, any one is ok. But the
price is different. The gap is bigger. Haha, you'd better check it.