请问potty training时是用哪种训练好？

是用独立的小potty训练
http://www.amazon.com/Baby-Bjorn-055121US-BabyBjorn-Potty/dp/B0009OLSZ8/ref=sr_1_1?ie=UTF8&s=baby-products&qid=1205865391&sr=1-1

还是用装在厕所上面的
http://www.amazon.com/BabyBjorn-Toilet-Trainer-White-Black/dp/B0009PAN7Q/ref=sr_1_2?ie=UTF8&s=baby-products&qid=1205865391&sr=1-2

还有出门时用哪种potty好？
http://www.amazon.com/Baby-Bjorn-050005US-BabyBj%C3%B6rn-Little/dp/B000056J78/ref=pd_rhf_p_t_3
http://www.amazon.com/Fisher-Price-L1496-Potty-On-the-Go/dp/B000K7IF1O/ref=pd_rhf_p_t_2