‎What is the correct setting for: Set Preferred Network Type. ?

I have the s9 plus.

For a couple months now I have had poor data connection - either no connection or H or 4g with no bars. 

‘’I’ve had to call att every few weeks to see if they can reset things  on their end in hopes for a better connection.

They just finally sent me a new replacement sim card to try. I just installed My signal strength is still very low and data slow.

I just called them again to ask what should my setting be for “set preferred network type” and all she could come up with was. If you can bring up and view web pages then leave it as the default.

However after all these months of attempting fixes for the poor reception, there is no way for me to know what is the real default setting.

Right now it is set with “ LTE/TD-SCDMA/UMTS” but I have no idea if this is default since it has been changed, and she didn’t know.

So my question is, does anyone know for sure what this setting needs to be or should be - since I still have poor reception.

thx