Without access to the technical details of the signal (cell site in use, band and signal strength, band width etc) it is only possible to make random guesses at what might be happening. First you need to ensure that you're comparing apples to apples, with respect to the band and cell site in use, band aggregation and so forth. On most Samsungs you dial *#0011# to access this info, but I've no clue how to get it on an Apple (or even if you can get it at all). 

Just dropping a phone can compromise cellular performance causing a difference between two otherwise identical phones.