Personally I would do a hybrid.
- Upstairs lighting
- Downstairs lighting
- Smoke & Hall lighting

If the smoke alarm trips off, only the hall lighting goes with it.

The hall tends to be the one with incandescent light bulbs and more
susceptible to B6 tripping. So when the hall trips off from a blown
bulb
all the rooms leading to it (up & down) still retain their lighting
capability.
Adding an EmLight to the hall circuit goes that useful bit further.

That meets the regs (314?) re minimised disruption from tripping.

Having an isolator to smoke alarms supplied by a lighting circuit is
useful so the alarms can be isolated when doing Ins Test part of PIR.
Which reminds me to add one at some point.
--
J.SB.