As with most medications of this type it will come down to a trial and error process to see which will help you. There is no "best" , try one to see it it works , if not , move on to the next one. Prozac was the first SSRI so you could chose based on that , or you could flip a coin maybe?
Weight gain can be a side effect of most SSRI I think. No way to tell if you will get it as everyone reacts differently.
Some quick side effects copied and pasted. Probably can be applied across the board for most SSRI
* diarrhea
* dizziness
* drowsiness
* dry mouth
* headache
* insomnia
* nausea
* tiredness or weakness
* trembling or shaking
* trouble sleeping
Less common
* agitation, anxiety, or nervousness
* back pain
* changes in taste sensations
* changes in vision, including blurred vision
* constipation
* decreased appetite or weight loss
* difficulty concentrating
* flushing or redness of skin, with feeling of warmth or heat
* heartburn
* increased appetite and weight gain
* increased sweating
* increased urination
* joint pain
* menstrual disorder
* stomach or abdominal cramps, gas, or pain
* vomiting
* yawning
Good luck with whichever you chose!