Weak mobile network

Question

Mobile network is very low (1 to 2 bars) when 3G is selected
Mobile network is comparatively good (3 to 4 bars) when 2G is selected
Settings -> Cellular -> Voice & data
I understand with previous experience (details in the below link) that this is due to weak 3G signal of the mobile provider.
Now i am very convinced that this is happening only while using nano sim cards (used in both iPhone 5S and MotoX).
While i was using normal sim card in my Samsung Galaxy S, this issue with 3G network was never there. Phone always used to handle
Requesting advice as to how do i approach this problem
1. Do i need to check in another mobile provider
2. What if the same issue persists in nano sim card of another mobile provider
https://forums.motorola.com/posts/46980d778d?page=1
As we can see in the conversation (detailed in the above link), I just want to keep 3G always "ON", and not rely on 2G network.
Also having 3G network On, increases my chances of tracking the phone 24 hours.
I have this expectation as my friend with same phone keeps 3G data always on. He does not have this big a problem with mobile network

Answer 1

Also the area you live in can cause connection issues - carriers no longer share so you cannot roam unto someone else's tower.    Hills can block signals and so can buildings - or areas inside buildings.    You can be right under a cell tower and not get cell service because its the wrong carrier as far as you are concerned.  
Carriers don't share because the government doesn't make them - so guess you are supposed to carry a bunch of cell phones or smart phones for best coverage.