Iphone 5 - Bluetooth 4.0 Iphone 6 - Bluetooth 4.2 Iphone 7 -...

Iphone 5 - Bluetooth 4.0
Iphone 6 - Bluetooth 4.2
Iphone 7 - Bluetooth 4.2

Samsung S6 - 4.2
Samsung S7 - 4.2
Samsung S8 - 5.0 (range increase)

Samsung with their Qualcomm Bluetooth is known for having trouble in the past and the only hope is 5.0 will bring the fixes they are after. Apple seems to have less dramas, but from what I can tell iphone 7's are more likely to have issues than an iphone 6s. Most of the issues are ios based from memory and 10.x update was meant to fix them, but it didn't for all... so there you go, doesn't matter what phone you purchase, there is always a chance you get a lemon. Bear in mind, if you buy a car and compare them on a dyno, they'll not be the same either...