Which version is best to upgrade to the iPhone 5 I use?

It is best to upgrade iPhone 5 to iOS 8.0, details are as follows;

This iOS is called "the most significant update released since the launch of the App Store", with hundreds of items launched Functions:

1. "Message" function improvements

1. Send voice, video and photos with one click and swipe

2. Provide group messaging options to name the conversation, add contacts, remove contacts or leave the conversation

3. Added detailed information view, providing "Do Not Disturb mode", location sharing and attachment view, etc.

2. "Photo" function improvements

1. Swipe in the smart editing tool to adjust light effects and colors

2. Fine-tune controls to adjust exposure, brightness, and contrast , highlights and shadows, etc.

3. You can search by date, location or album name, or use smart suggestions

4. Provide slow-motion videos, burst snapshots, and panoramic photos and time-lapse photography smart albums

5. "Photos" directly supports third-party filters and editing tools

6. Your photos and metadata in iPhoto will be migrated to "photo". Albums, journals, and slideshows are converted into photo albums containing only photos.