Flexible grout or silicone?
The cons against silicone are that I'm bound to get it smeared over the nicely painted ceiling and it's fiddly to get up there to work in detail with the old Fugenbois (it just is - would take ages to explain why in detail, but it's over the bath which is tucked partly into a recess).
Otherwise I would have defaulted to silicone...
Grout OTOH wipes off paint nicely...