Are you on a different band with the Note 4? The 5C has always been a good RF performer.
However, it can be said that Samsung has made HUGE strides in their RF performance, especially after they made the jump to using a metal "band" around the device. Note 4 was the first major Sammy device with the metal band.
iPhone 5C: Quad Band GSM; LTE: 1, 2, 3, 4, 5, 8, 13, 17, 19, 20, 25; UMTS: Band I (2100), Band II (1900), Band IV (1700/2100), Band V (850), Band VIII (900)
Note 4: Quad Band GSM; LTE: 1, 2, 3, 4, 5, 7, 8, 12, 17; UMTS: Band I (2100), Band II (1900), Band IV (1700/2100), Band V (850)
The Note 4 has more bands in the sense of low frequency since it has the Band 12, but the iPhone 5C has more depth.
So I assume it's the same LTE network.
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My Note 4 is excellent when talking about signal strength. With a wide range of volume adjustment it's great as a phone on AT&T.
My iPhone's have also been good except for the lower volume on the iPhone 6 series both 6 and 6 Plus could benefit from a boost in volume. Clarity is good almost as clear as my Nexus 6 which has the best performing phone I've ever had.
That's because of the Nexus 6 being made by Moto, who are known for their radios? Which of your phones has the best battery life? What about efficiency? Least buggy one? I thought the Note 4 was the better of the two between the Nexus 6 and the N4, but that was back in October I said that. Now, I am beginning to rethink my decision. Samsung hasn't supported the Note 4 on T-Mobile so great these days.