iPhone 6s problems

With Personal Hotspot connectivity concerns, see this If Personal Hotspot is not working on your iPhone or iPad (Wi-Fi + Cellular) - Apple Support

Also, what I can suggest to try is: Reset your Network Settings.

Go to Settings > General > Reset > Reset Network Settings. This also resets Wi-Fi networks and passwords, cellular settings, and VPN and APN settings that you've used before.

My iPhone glitches and occasionally Powers off by itself as it also has a very glitchy keyboard and will often get “ghost touch” or just freeze

With regard to other issues you have mentioned, I would suggest you take it to Apple to find out exactly. You could restore to Factory Settings and see if that will fix any/all of the issues. Please backup and read the following article, before you try anything.

Restore your iPhone, iPad, or iPod to factory settings - Apple Support

what iPhone do you recommend if my phone is unable to be fixed ?

This would depend on your budget and personal preferences (screen size, storage capacity, etc.) and how you plan to use it.

iPhone - Compare Models - Apple