It depends on whether, known or unknown to you, depression is a problem. Effexor is a stimulating antidepressant that makes some people, especially those with primary anxiety, more anxious, and wellbutrin is a very stimulating antidepressant. Sometimes wellbutrin is combined with an ssri such as Paxil to combat the weight gain. So you might want to try the Zoloft or maybe Lexapro and see what happens.
I also was taking Paxil and I switched because I gained 30lbs and had the shakes and some other weird side effects. I went on Effexor 37.5mg and did very well on it.