I'm on Verizon and have the iPhone 4s too... I have the Vapor Pro Stealth and love it. Haven't taken it off my phone since I got it, about 2 months ago. No reception issues.
I would get this, more power!... https://forums.imore.com/e?link=http%3A%2F%2Fstore.imore.com%2Fmophie-juice-pack-plus%2F8A37A7976.htm%3Futm_campaign%3Dcommunity%26utm_source%3Dvb_im%26utm_medium%3Dcontent&token=87PuQWEf