Using groups question

I have created a few groups with some Hue lights.
Is it best to have the retain, transition etc attributes assigned to each device or just to the Group?

This:

Devices:
‘0x00178801105dcb12’:
friendly_name: light_1
retain: false
transition: 0.4

‘0x00178801105drt13’:
friendly_name: light_2
retain: false
transition: 0.4

Groups:
‘1’:
friendly_name: light_group
optimistic: true
devices:
- ‘0x00178801105dcb12’
- ‘0x00178801105drt13’

Or this:

Devices:

‘0x00178801105dcb12’:
friendly_name: light_1

‘0x00178801105drt13’:
friendly_name: light_2

Groups:
‘1’:
friendly_name: light_group
retain: false
transition: 0.4
optimistic: true
devices:
- ‘0x00178801105dcb12’
- ‘0x00178801105drt13’