I have a 5 on Verizon and had both wifi and cellular reception issues. A 4S and a 4 in the same spot, also on Verizon, had no issues. The wifi was so bad that my phone would drop the connection sitting two feet from the router. After *many* trips to the Genius Bar and two phone swaps I figured out that the issue was with the cases I was using. Any case with metal drastically cut my reception. Non-metal cases are okay but reception is best (especially in weak coverage areas) with a bumper or no case at all. Your mileage may vary, but I thought I'd share.
Liz